BIVALVIA. 



101 



Mysca pictobum. Turt. Brit. Biv., p. 245, 1822. 



— Deshayesii. Brown. Illust. Brit. Conch., p, 81, pi. 32, figs. 1 — 4. 



— — Rossm. Icon. Land und Sussw. Moll., p. 23, pi. 13, fig. 197. 



— LONGIROSTEIS. Ziegl. in Rossm. Iconog., pt. 3, p. 2t), pi. 14, fig. 200, and pt. 12, 



pi. 54, fig. 38. 

 Ency. Meth., t. 248, fig. 4. 



Spec. Char. Testa transversa, elongatd, subovatd, inaquilaterd, antice rotundata, 

 postice, anr/ulafd, vix rostrata ; margine dorsali et ventrali suhrectd. 



Shell transversely ovate, elongate, inequilateral ; anterior side rounded, posterior 

 angulated, scarcely rostrated ; dorsal and ventral margins nearly straight. 



Length, 2 inches. 



Locality. Grays, Cropthorn. Recent, Britain, France. 



This shell appears very rare as a British fossil ; one specimen in the cabinet of 

 Mr. Pickering is of a form that may be determined without mucli hesitation as belong- 

 ing to this species, and resembles rather the thinner variety of the recent shell. The 

 principal or perhaps only difference observable between this and the preceding species 

 in the fossil state, is a more elongated dorsal area, less sloping on the posterior side, 

 so that the ventral margin is more parallel with the upper edge than in TJ. tumidus. 

 A specimen in the British Museum, from the same locality, seems to possess the like 

 determinable characters, and one in the Museum of the Geological Society, presented 

 by Mr. Strickland as from Cropthorn appears to be of this species. These specimens 

 are all that I have seen, they mostly resemble fig. 766, Rossmasler. 



Anodont.a., Cuvier, 1798. 



MuscuLUs (sp.). Lister. 

 Mytilus (sp.). Linn. 



Ll.MN.«A and LiMNiEODEKMA (sp.). 



1791. 

 Anodontites. Brug., 1799. 

 DiPSAS. Leach, 1814. 

 Appius. Id. MSS., fide Gray, 

 Anodon. Oken., 1815. 



Poli, 



Cristaria. Schum., 1817. 

 Strophitus. Rafinesque, 1820. 

 Lastena. Id. 



Symphynota (sp.). Lea., 1832. 

 Odatelia. Rafinesque, 1832. 

 Lamproscapha. Swains., 1840. 

 Hemiodon. Id. 



Patularia. Id. 



Generic Character. Shell equivalve, inequilateral, ovate, transverse, usually thin, 

 more or less eared, and closed ; smooth, and in the recent state covered with an 

 epidermis generally eroded at the umbones. Hinge linear, edentulous, or with one 

 elongated lamina on the posterior side. Ligament external. Impression of the mantle 

 without a sinus. 



The animal of this genus closely resembles that of the preceding one, being furnished 

 with a large fleshy, compressed foot, and the hinder part of the mantle is ornamented 

 with short and pointed tentacles ; anal opening is large, and the margin plain. 



