Rivista Italiana di Paleontologia e Stratigrafia volume I uó pagrne 359-368 Novembre 2002 MARM ARON I A AN G I O LIN II, NE\T GENUS AND NE\T SPECIES OF BAKEVELLIIDAE (PTERIOIDA, BIVALVIA) FROM THE MIDDLE PERMIAN OF CHIOS (GREECE) CRISTIANO LARGHI Receit,ed February 21, 20A2; accepted July 23,2002 Key-roords: Chios, Greece, Bivalvia, Bakevelliidae, Guadalupi- an, Middle Permian. Riasswnto. I "Calcari a Gymnocodiacee" guadalupiani (Permi- ano Medio), affioranti nella parte nordorientale dell'isola Greca di Chio (Egeo orientale), sono tra i più fossiliferi della Tetide occidentale. Essi contengono ricche associazìoni a coralli, brachiopodi, molluschi, alghe calcaree, foraminiferi e ostracodi, tuttavia, mentre i brachiopodi e i foraminiferi sono stati oggetto di studi sistematici, scarsa atten- zione è stata dedicata, sino ad ora, alle faune a molluschi. Nel presente lavoro viene istituito il nuovo genere Marmaronia con specie tipo Marmaronia angiolinii n. sp. per comprendere alcuni bivalvi della famiglia delle Bakevelliidae King, 1 850, rinvenuti nelle suc- cessioni del Guadalupiano medio della località di Marmaro. Marmaro- nia angiolinii n. gen. n. sp. é fortemente inequivalve, con valr.e clie dif- feriscono per convessità, sviluppo degli umbonì e ornamenrazione. La valva sinistra presenra un solco radiale che partendo dall'umbone giunge al margine ventrale ed é ornata da robuste coste radiali; la valva destra presenta rughe di crescita concentriche e debolissime coste radi- ali visibili nella parte posteriore della conchiglia dei primi stadi di crescita di alcuni esemplari; entrambe le valve mostrano un'ala posteri- ore esPansa. Nel presente lavoro vengono inoltre discusse brevemente due ipotesi riguardanti un possibile adattamento epi- o endobissa to di Mar- mdronLd,. Abstract. The Guadalupian (Middle Permian) "Gymnocodi- acean Limestones" cropping out in rhe north-eastern part of the Greek island of Chios (eastern Aegean Sea) are amongst rhe most fossilifer- ous in the western Tethys. They contain rich assemblages of corals, brachiopods, molluscs, calcareous algae, foramìnifers and osrracods. Scant attention was given till now to mollusc faunas compared with brachiopods and foraminifers. In rhe presenr paper the new genus Marmaronia, with type-specìes M. angiolinil n. sp., is established to distinguish some bivalves of the Bakevelliidae King, 1850, from the middle Guadalupian successions of the Marmaro locality in Chios Island. M. angiolinii n. gen. n. sp. is strongly inequivalve, with valves differing in convexity, umbo developmenr and ornamentation. The left valve shows a radial furrow running from the anterior part of the umbonal region anreroventrally and is ornamented by strong radial costae; the right valve is ornamented by concentric sculpture and by thin rugae in the first growth srages of the posterior part of the shell. Both valves have a *ide posrerior wing. Two hypotheses concerning the epi- or endobyssate adaptation of Marmaronia are also discussed briefly in the present paper. lntroduction The study of Permian bivalves of the Tethyan province was neglecred compared with other fossil groups such as foraminifers, conodonts and bra- chiopods. The majority of the limited literature address- es the Eastern Tethys (see Hayami 8t Kase 1977; Nakazawa & Newell 1968; Wanner 1922, 1.940); Permi- an bivalves in the western parr of the Tethyan province s-ere described by Gemmellaro (1892), Termier et al. (1977), Boyd & Newell (1979) and recently by Dickins (1999\. In the last few decades the importance of Permian bivalve faunas in the fields of palaeoecology. palaeobio- geography and biostratigraphy has been recognized. The discovery of a connecrion between the cold water Eurydesma fauna and the late Paleozoic Gond- wanan glaciations, for example, was useful for the inter- pretation of Permian climate changes, as well as for global correlations (Harrington 1955; Dickins L957, 1978, t984). Moreover, the bivalve assemblases associared s/irh the transgression on the mid-Permian unconformity, are found in many parts of the world, including Australia, New Zealand, the northern Russian Region, the central and southern United States and recently Oman (Dickins 1997, 1999). These faunas are characrerised by the appearance of new pecrinacea and permophorids, and by the development of multivincular pterioid forms such as Babevellia (Dickins 1997). From a biostratigraphic point of view, some gen- era discovered for the first time in the Permian succes- sions have acquired roday a grear imporrance nor only in the Permian, but also in the Lower Triassic. Some species atrribured to rhe genvs To,wdpterìa Nakazawa & Newell, 1968, for example, have now a great biostratigraphic importance in the Tethyan province. In particular T. schytica (Wirth) was men- Dipartimento di Scienze della Terra, via Mangiagallì 34,20133 Milano, Italy, e-mail: crìstiano.larghi@unimi.it 364 Fig. 1 - Location map of Chios ìn the Aegean area. tioned for the first time in the Eastern Tethys deposits of western China (Wirth 1936) and later in the Dolomites (Broglio Loriga et al. 1983). Later this species presence was confirmed in the basal Lower Tri- assic of south-western China (Chen 1980). Today Z schytica is considered an important index for Lower Tri- assic global correlations (Shen et al. 1995, Yin Er Tong 1998; Kozur 1998). Today the knowledge on bivalves in some areas of the Tethys is almost non-existent and according to Yancey (19S5), a high degree of endemism shown by some Permian faunas could be only the result of lack of knowledge. Perhaps new studies on bivalves will permit to discover new taxa useful for the correlations of Per- mian benthonic faunas. This work is part of wider investigations on the Palaeozoic successions of Chios Island, involving many researchers from the Dipartimento di Scienze della Terra of the Università di Milano and from other Italian and European lJniversities. Previous works and geological setting. The island of Chios, one of the largest in Greece, is located in the eastern Aegean Sea a few kilometres from the Turkish coast of the Karaburun peninsula (Fig. 1). According to many authors (Herget & Roth 1968, Besenecker et al. 1968, 1,971) two tectono-stratigraphi- cal units can be distinguished on Chios Island: an autochthonous unit and an overthrust of an allochtho- nous unit. The lower unit consists of a thick Palaeozoíc succession, composed of terrigenous rocks, cherts, vol- canics and limestones (the last dated-from Silurian to Carboniferous), which is overiain by a Meso-Cenozoic succession. The allochthonous unit comprises an Upper Carboniferous to Upper Permian sequence, underlying a Liassic shallow-water carbonate platform. Red siltstones of uncertain age separate them (Kauffmann 1969; Bese- necker et al. 1968). The study area described in this paper belongs to the allocthonous unit. A Middle Permian carbonate sequence crops out specifically near Marmaro, Agrelias and Parpanda. These very fossiliferous limestones were called "Gymnocodi- acean limestones" (Gymnocodiaceen-Kalke) by Kauff- mann (1969) (Fig.2). Fossils consist of calcareous algae, corals, molluscs, echinoids, brachiopods, fusulinids, smaller foraminifers, ostracods and conodonts. Flajs et al. (1,996a) provided a list of the most fre- quent algae which are Gymnocodium belleropbontis, Per- m o c a I c w I w s t e xa,n urrî., M i z z i a rt e I e b itan a an d P s e w d oo erm i - porella sodalica, but until now no systematic study of these algae has been produced. On the contrary the sys- tematics of the rich assemblage of silicified brachiopods from some levels of the "Gymnocodiacean limestones" near Marmaro, was studied by Grant (1,993). An age for the "Gymnocodiacean limestones" was given by Kahler (1987) who studied foraminifers sam- pled by Kauffman during his doctoral thesis. FIe men- tioned the presence of the foraminifers Nankinella infla- ta and Eoverbeehina intermedia, that correspond to the Middle Permian, in the "Gymnocodiacean limestones" of the Marmaro section. According to Flajs et aI. (1996a) the "Gymnocodi- Ftg.2 - Simplified geological map of northeastern Chios (rectangle in fig. 1) showing the investigated area and the outcrops of "Gym- nocodiacean limestones" (from Flajs et aL.7996a, modified). 0 D -tPou úQ îr\É, L:H ol "Gy-'mnocodiaceau Lilresl nsu Besenecker el al. I 97 I ) t Rlt ii"i I rr<- I I )utcfops / orkì Marmaronia angiolinii 361 acean limestones" exposed in the Marmaro section belong either to the Verbeekina Zone or to the NeoschwagerinaZone, which correspond to the middle Guadalupian. No work was devoted to the mollusc faunas uo ro now: The Marmaro section. One of the best exposed outcrops of the "Gy-- nocodiacean limestones" is located on rhe easrern side of the Marmaro beach (Fig. 2). The Marmaro secrion (Fig. 3), approximately 32 meters thick, was divided into 5 Units by Flajs et al. (1,996a). The stratigraphy of the present paper is based on that work. Unit 1 reaches a thickness up to rhree meters. This unit is composed of dark grey to black or brown thin-bedded limesrones, which include mud- stones, wackestones, packstones, floatstones and frame- stones. It consists of 30-60 cm thick individual layers of yellow-brown limestones with corals (Multithecopora sp.) and intercalations of brachiopods and black lime- stones with molluscs and foraminifers; the amount of corals decreases towards the top of the unit, while at the base corals form biostromes. Foraminifers, calcareous algae and a variety of encrusting micro-organisms form the bulk of the microfossiliferous assemblage. Some coquina beds suggesr rempestite deposits and red and green algae, which locally form algal packstones, indi- cate moderate water depths (Flajs et aI. 1996b). Unit 2 consists mainly of grey to brown calcare- ous marls up to 2 m thick. Abundant richtofeniid bra- chiopods, many bryozoans, echinoderms and kirkby- acean and bairdiacean ostracods, which are supposed to indicate calm warer conditions (Flajs et aI. 1996b), are present locally. Richthofeniids in the upper levels form a massive reef limestone up ro 6 m thick, called Unit 3. Calcareous marls with à yery high fossil conrenr (Unit a) separaîe the richthofeniid bank from regularly bedded limestones containing calcareous algae and oncoids (Unit 5) which represent the end of the Mar- maro Permian sequence. Many specimens of a single species of bivalve can be collected in all the units of the "Gymnocodiacean limestones", except for Unit 3. Systematics analyses showed that these bivalves belong to a new genus and a new species for which the name Marmaronia angiolinii ìs introduced. The Types of Marmaronia angiolinii n. gen. n. sp. were collected in the upper part of Unit 1 (fig. 3). Some specimens of Marmaronia angiolinii (MPUM8605A-D) were collected also by L. Angiolini and L. Carabelli (Dipartimento di Scienze della Terra, Università degli Studi di Milano) in the locality of sam- ple USMN9592 of section II, described by Grant (1993) in the region of Agrelia (Parpanda). Faunal and sedimentoloeical features in the mud- Fig. 3 - Stratigraphical section of "Gymnocodiacean Limestones" outcropping in rhe Marmaro bay (from Flajs et al. 1996a, modified). stones and marls of Unit 1 (the Stratum Typicum o{ Marmaronia angiolinii n. gen. n. sp.) suggest calm waters and a lagoonal environmenr, but probably the coquinas of this unit indicate that this environment was subjected to periodically heary and deep-reaching storms. Bivalved specimens of Marmaronia are present in the mudstones of Unit 1, together with spines of large quasi-infaunal brachiopods. On the contrary, in the coquinas valves are always disarticulated, often selected by transport (actua11y some fossil concentrarions are composed exclusively of right valves). K lJ nit lJnit w Iww w I trpe scrics t hvcls K ['lrrnrarrnia I*egg*d trtr Llmestone m Marl ffi Coquinoid I e\'e i 362 Systematic Paleontology. Illustrated and described specimens are housed in the collec- tions of the Dipartimento di Scìenze della Terra, Università degli Studi di Milano, Museo di Paleontologia, via Mangiagalli 34, Milano, Italy (numbers with the prefix MPUM). Phylum Mollusca Ciass Bivalvia Linné, 1758 (Buonanni, 1681) Subclass Pteriomorph a Beurlen, 1.9 4 4 Order Pterioida Newell, 1965 Suborder Pteriina Newell, 1965 Superfamily Pteriacea Gray, 1.847 (1820) Family Bakevelliidae King, 1850 Preliminary remarks The important family of Bakevelliidae (King, 1995), which includes highly inequilateral Pterioida with a usually rhombic to trapezoidal outline, originated in the Permian and flourished in the Cretaceous. According to Muster (1995) important diagnostic features of the family are the outline (defined by param- eters diagonal, maximum length of the body, length of the posterior wing, and obliquity), shell ornamentation, wing shape, position and shape of the umbones, hinge, and muscle scars. Marmaronia n. gen., showing all the features of this family, represents one of the most ancient members ^f thi" o"ntrnb'- "r' Marmaronia n. gen. is similar to some genera of Cassianellidae Ichikawa, 1958, for the presence of a well- developed radial furrow on the left valve; however, the internal septum, important character of the Cassianelli- dae, is absent. The records of Cassianellidae in the Permian suc- cessions are still sporadic and based on incomplete sPec- imens in which the important internal characters are often not visible. Genus Marmaronia n. gen. Type species,4larmaronia angiolinii n. sp. Etymology. Genus named from the locality of Marmaro (Mcrppcrpo), island of Chios, Greece. Composition of the genus. At present the genus is composed only by the type species Marmaronia angioLinii n. sp. Diagnosis. Shell small, oblique, prosocline, from rhombic to trapeziform, inequilateral and posteriorly alate, strongly inequivalve; shell sinuated for byssus in the antero-ventral margin. Left valve strongly convex, with prominent umbo ornamented by strong radial costae, anterior not lobate but with a radial furrow running from the anterior part of the umbonal region to the ventral margin. Right valve less convex, with prominent umbo, without a true anterior auricle, but with an anterior lobe depressed in comparison with the umbonal region; right valve ornamented by a concenrric sculpture and by feq thin, filiform costae in the posterior part of the shell body, present only in the first growth stages; hinge consisting of two (or perhaps three in the right valve) cardinal teeth and one slen- der, long, posterior lateral tooth parallel to the hinge margin. Ligament area straight and rather wide, ligament multivincular. Discussion. The new genus is similar to the genus Towapteria Nakazawa Er Neweil, 1968 established on the basis of some specimens from the Japanese Middle Per- mian associations of the Tenjinnoki and Kanokura For- marions (Nakazawa 8r Newell, 1968), and later discov- ered in other Permian and Lower Triassic localities of the Western and Eastern Tethys. Muster (1,995), in his emended diagnosis of the genss Torl)apteria, defined this genus as a Bakevellidae without radial ribs on the anterior wing. However, this is true only for the right valve because the holotype of the type species T. nipponica Nakazawa & Newell, 1968 (P1.3 fig.8), which is a left valve, shows radial ribs in the anrerior part of the shell (which does not have a real anterior wing or lobe, also according to the original C. Larghi PLATE 1 Fig. 1 - Litrle slab from the coquinoid levels (upper part of Unit i, Marmaro section) with valves of Marmaronia angiolinii n. gen. n. sp. (x 1). Fig.2 - Marrnaronia angiolinii n. gen. n. sp., left valves from Agrelia (x 1). Fig.3a,b -Marmaroniaangioliniin.gen.n.sp.,paratypeMPUMS6O3N, leftvalve; 3a:lateralview(x1.5);3b:frontalview(x2). Fig. 4- Marmaronia angioLinii n. gen. n. sp., paratype MPUM8604D, right valve, internal view (x 1.5). Fig. 5 - Little slab from the upper part of Unit 1, Marmaro section, on the right the paratype MPUM86O2 (the same specimen in fig. 6)(x 1.5). Fig. 6 - Marmaronia angiolinii n. gen. n. sp., paratype MPUM86O2, articulated specimen, lateral view of the right valve (x 3). Fig.7 - Marmaronia angiolinii n. gen. n. sp., paratype MPUM8603M, left valve, lateral view (x 1.5). Fig.8 - Marmaronia angiolinii n. gen. n. sp., pararype MPUM8604G, right valve, oblique view of the partially broken hinge (see arrow) (x 2). Fig. 9 - Little slab with right valves oÍ Marmaronia angiolinii n. gen. n. sp., the arrow indicates the paratype MPUM8604A (x 1.5). Fig. 1O-12, 16 - Marmaronia angíolinii n. gen. n. sp., holotype MPUM86O1, articulated specimen; 1O: lateral view of the left valve (x 2); 11: frontal view (x2'1;12: dorsal view (x 2); 16: ligament area showing the ligamental pits (marked by arrows) (x 8). Fig. 13 - Little slab from the coquinoid levels (upper part of Unit 1, Marmaro section), with valves oÍ Marmaronia angiolinii n' gen. n. sp., the arrow indicates the paratype MPUM8604G (see also fig. 8) (x 1). Fig. 14 - Marmaronia angiolinii n. gen. n. sp., paratype MPUM86O4G, left valve, hinge area with cardinal teeth marked by arrows (the tooth on the left is broken) (x 3). Fig. 15a, b - Marmaronia angìolinìi n. gen. n. sp., paratype MPUM86O3\( left valve; 15a: internal view with cardinal teeth marked by arrows (x 8,1r l5b: enlargement of rhe hinge tx 20) Pl. 1 JI arnt aronitt angìctltn ít i63 364 C. Largbi description by Nakazawa Er Newell 1968; p. 58). The original diagnosis of Towapteria by Nakazawa & Newell f 1968) can be considered still valid. The new genus Marmaronia is distinguished from Towapteria in the less pteriiform outline (because of the presence of a more expanded posterior wing, with a less incised sinus), in a wider ligament area, in the prominent umbo of the right valve (beak located above the hinge margin) and in the ornamentation of the right valve. The radial costulation is very slight in the first gros/th stages and absent in the adult stage. Costigervillia Cox & Arkell, 1948 differs from Marmaronia in the outline, in the more developed obliq- uity of the shell, in the presence of an anterior wing on the left valve and of few but strong ribs on the right valve. Single valves of Marmaronia n. gen. are similar to the valves of some genera such as Arcapicwla Cox, 1964 (right valve) or Oxytoma Meek, 1864 (left valve). Occurence. "Gymnocodiacean limestones" sensu Kauffmann (1,969) of Chios Island (Greece). Age. Middle Guadalupian (Middle Permian). Marmaronia angiolinii n. sp. (Plate 1) Material. Total: 43 specimens. 39 specimens from Marmaro (MPUMS601, 2; MPUM8603A-Z, u, B; MPUM8604A-L) and 4 spec- imens From Agrelia (MPUM8605A-D). Type series (28 specimens). Hololype. A bivalved complete specimen: MPUM8601 (Pl. 1, fig.10-12, 16). Paratypes. Bivalved complete specimen: MPUM8602; left valves (16 specimens): MPUM8603A, g, D-F, J, K, M, N, O-Q, U, Y \l,Z; righr valves (10 specimens): MPUM8604A-L. Etymology. Species named in honour of Lucia Angiolini. Stratum Typicum and Locus Typicus. The locus typicus is the Marmaro section and the Stratum Typicum is the upper part of Unit 1 sensu Flajs et al. (1996a). Diagnosis. As for the Genus. Description. Shell small, oblique, prosocline, from rhombic to trapeziform, inequilateral and posteriorly alate. Ratio of height to length about 0.9. Strongiy inequivalve, left valve strongly convex, anterior not lobate, but with a radial furrow running from the anteri- or part of the umbonal region to the ventral margin; right valve less convex, without a true anterior auricle, but with an anterior lobe depressed in comparison with the umbonal region. Both umbones are narro.wly rounded, protruding and placed anteriorly. Dorsal margin long and straight, a little shorter than the length of the shell. Valves discordant, right valve smaller than the left. No subauricular notch, only faint traces of a sinuation in the antero-lateral margin. ' Posterior wing very wide separated from the body of the shell by a very shallow sinus. Ligament area rarher developed, perpendicular to the commissure plane of valves, wider in the right valve than the left, even if the left is wider and more convex. Ligament multivincular, with several weak, subrectangu- lar or rarely subtrigonal pits; on some specimens (MPUM8601, MPUM8603N) the pits are at least five, and one of them is located under the beaks. Hinge consisting of two cardinal teeth on the left valve, (one under the beak and one strong anterior car- dinal, Fig. 4) and one slender, long, posîerior lateral tooth parallel to the hinge margin. On the right valve hinge consisting of two (or three) cardinal teeth and, like in the left valve, one slender, long, posterior lateral tooth parallel to the hinge margin. Surface of left valve sculptured by radial costae of one or two orders and by concentric costae over shell body and posterior wing, radials more or less scaly and sometimes nodose at intersections with concentric costae. On the larger specimens there are 6-9 costae near the ventral margin, between the radial umbonal sulcus and the posterior margin of the shell body (which sepa- rates the body margin from the posterior wing). Before the sulcus there are 7-8 strong radial costae; the posteri- or wing has a reticulate ornamentation because of the intersections between 7-8 weak radial costae and the growth rugae. There are costae of the first and second order, the latter nre and present only in specimens larg- er than 7 mm. Right valve ornamented by concentric growth rugae and in some specimens, in the first growth stages, by few very thin costae near the posterior margin of the shell body (this radial costulation is perhaps present Fig. 4 - Reconstruction (from camera-lucida, shaded) of the cardi- nal teeth (marked by arrows) in two left valves, A: speci- men 8603D. B: soecimen 8603\( Marmaronia angioltnii 365 Fig 5 - Hypothetical endobyssate life habit of Marmaronia only in few specimens because it has been removed b) abrasion or iÀ/eathering). A displacement of the radial ornaments visible on the MPUM86O3F specimen might indicate that the organism survived a trauma. Muscle scars and pallial line not observed. Dimensions (in cm). Specimen Length Height Thickness MPUM8601 (Holotype, bivah.ed specimen) 1'.4 1.3 MPUM8602 (paratype, bivrlved'pecimen; corals, brachiopods and calcareous algae, it lived in very shallow waters. The morphology of Marmaronìa suggests two possible different strategies of byssal attachment: epibyssate or endobyssate habit. Following the model of Kauffman (1969) which correlates the shell shape with the exposure to currents, Marmaronia shows a rather hydrodinamically stream- lined shell. Perhaps Marmaronia lived as an epibyssate in the most exposed lagoonal environments or in coralline patch reefs, attached to the biostromes made up of syringoporid corals (Mwlthitecopora sp.), brachiopods and calcareous algae. Yet this epibyssate habit is most suitable for bivalves which have, unlike Marmaronta, a developed anterior auricular sulcus and a byssal sinus (see also: Stanley 1972). The model proposed by Seilacher (1983) for the byssate Bakevelliidae seems most suitable for Marmaro- nia. According to this model Marmaronia was endobyssate, partly buried in mud. It would have lived reclined flatly in the sediment, and the strongly inequiv- alved shell could be evidence of this way of hfe. Marma- ronia rested on the left valve, which is more convex and bears stronger sculpture to increase adhesion to the sed- iment (Fig. 5). The ligament area of Marmaronia is more developed than in similar epibyssate forms because the ligament must ha\re acted against the sediment pressure. This way of life seems to be confirmed by tapho- nomic analyses: the mud levels of the upper part of Unit 1, in which bivalved specimens can be collected, could represent the levels in which the bivalves lived. Acknou'ledgemen ts. I n.ish to acknowledge M. Balini for fruit- ful discussions and a preliminary rer.iew of the manuscript, G. Chiodi and A. Rizzi for providing the photographs, E. Gozzi and N. Manto- vani for the computer assistance and technical suPport, C. Cortzzato for rmproving rhe English 'ersion. I am indebted to G. Kauffmann, who gave me useful informa- tion about the locality of Marmaro and bibliographic material, with L. Angiolini and L. Carabelli, for joint field-work and for providing the specimens from Agrelia. I heartly thank J. M. Dickins and K. Nakaza- - . f^. ^-;,;^,11,, .-.li-- ,1".\\J IUI !lltlLal,) l(dul.lÉ trl( mJnUSCflpt, A ver,v special thank you to mv mentor M. Gaetani, who encouraged me to study the Palaeozoic of Chios. Financial supporl provided by COFIN 2A0A/2001', pro;ect ot Prof. M. Gaetani. 0.8 0.9 MPUM86O3M (paratype, left valve) 1.9 1.7 MPUM86O3N (paratype, left valve) 1.3 MPUM86O4D (paratype, right valve) Discussion. Apart for the generic characters, Towapteria nipponica Nakazawa & Newell, 1968 differs f rom Marmaronia angiolinii n. gen. n. sp. in having mor. numerous and differentiated (to 3rd order) radial costat on the ieft valve. There are some similarities between the first onto' genetic stages of Geruillaria alaeformis (Sowerby' 1819) and Marmaronia angiolinii n. gen. n. sp. but the left valve of this species shows a distinct anterior wing. Marmaronia angiolinii n. gen. n. sp. is similar externally to CassìanelLa decussata (Muenster, 1834), but the latter shows a developed anterior auricle. Only the right valve of Marmaronia angiolinii n. gen. n. sp. is similar to the right valve of Baleeoellia cer- atophaga (Schlotheim, 1816), but can be distinguished by a more prominent umbo and a wider posterior wing. Occurrence and Age. The same as the genus. 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