BIVALVIA. 45 



margin ; the exterior is covered with numerous irregular striae or striated costae, 

 rough or scabrous, radiating in an undulating direction, extending from the extreme 

 edge of the posterior side to the anterior, where, for a small space, it is naked or 

 destitute of striae, those on the posterior are fine and closer set, becoming larger and 

 more distant as they approach the anterior, where they are rough and project beyond 

 the margin. The hinge line is less oblique than in exilis, and is narrower, which per- 

 haps it would be, if not a different species, corresponding thus with the more narrow 

 form of the shell, but the ligamental area is deeper from the umbo inwardly, while the 

 gape on both sides is larger than in that shell, and the whole contour in this is so dif- 

 ferent that, judging from the specimens which I possess, they cannot be united without 

 an extension of variation greater than is generally permitted to species of this genus. 



In the recent state, in the more northern parts of the British seas, it attains a greater 

 magnitude than is given by the dimensions of our fossil, which may not, possibly, be a 

 full-grown individual, although its gape is wide, a character of the adult shell ; it is said 

 one inch and three quarters is not an uncommon size in the recent British specimens, 

 whilst those found at Guernsey are less, resembling in this peculiar our Crag fossil. 



3. LIMA LOSCOMBII, G. Sowerby. Tab. VII, fig. 1, a c. 



PECTEN FRAGILIS. Mont, (not Chemnitz). Test. Brit. Sup., p. 62, 1808. 



OSTREA FKAGILIS. Turt. Conch. Diet., p. 131, 1816. 



LIMA BULLATA. Turt. (not OSTREA BULLATA, Born.). Brit. Biv., p. 217, t. 17, figs. 4, 5. 



Thorpe. Brit. Mar. Conch., p. 114, 1844. 



Phil. En. Moll. Sic., vol. ii, p. 56, t. 16, fig. 2, 1844. 



LOSCOMBII. G. Sow. Genera of Shells, No. 17, LIMA, fig. 4. 



Reeve. Conch. Syst., pi. 112, fig. 4. 



G. Sow. Thesaur. Conch., vol. i, p. 86, pi. 22, figs. 2022. 



Loven. Ind. Moll. Scand., p. 32, 1846. 



Forb. and Hani. Hist, of Brit. Moll., vol. ii, p. 265, pi. .53, figs. 13. 



Alder. Cat. Moll. North, and Durh., p. 78, 1848. 



FRAGILIS. Brown. Illust. Conch. Gr. Brit., pi. 31, figs. 6-7, 1827. 



Forbes. Mag. Nat. Hist., vol. viii, p. 594, fig. 65. 



Id. Malac. Monen. p. 40, 1838. 

 S. Wood. Mag. Nat. Hist., New Series, vol. iii, p. 235, pi. 3, fig. 3, 1839. 



Spec. Char. Testa tumidd, odlique-ovatd, intequilaterd, tenui, fragili ; utroque latere 

 perparvulum hiante, striatd, striis tenuissimis, alternatis, undulatis, cardine oUiquo. 



Shell tumid, obliquely ovate, inequilateral, thin and fragile ; very slightly gaping 

 on either side, covered with fine striae, slightly undulating, and alternately larger and 

 smaller ; cardinal area oblique and small. 

 Greatest Diameter, f of an inch. 

 Locality. Cor. Crag, Sutton and Ramsholt. 

 Red Crag, Walton Naze. 



Recent, Britain, Norway, and Mediterranean. 



