84 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



rostrata, attenuata, area lata, plicis duobus longitudinalibus ; latere antico mhcompresso, 

 eUiptico ciirvato, plicisqtie regularihus et longitudinalibus. 



Shell transversely elongated, very insequilateral ; umbones placed anterior to the 

 middle of the valves, small, depressed, and anterior ; posterior side rostrated or attenuated, 

 and much elongated ; area large and wide, with two longitudinal ridges, in addition to a 

 distinct marginal ridge which separates the area from the other portion of the shell ; 

 anterior side rather compressed, its border is curved elliptically ; the anterior portion of 

 the sides of the valves have regular, longitudinal ridges and furrows, which disappear 

 posterior to the umbones ; the oblique sulcation which proceeds downwards from the 

 umbones in all examples of Cercomya is only faintly impressed. 



The specimen figured has the general form of the shell unusually well preserved, but 

 the test has disappeared ; the very inequilateral figure, with the attenuation and elongation 

 of the posterior side, will readily distinguish it from Anatina undiilata, Sow., as also from 

 most other examples of the genus. 



Height, one third the length ; diameter through both the valves, one fourth the 

 length. 



Geological Positions and Localities. It occurs rarely in the Cornbrash of Scarborough. 

 Professor Phillips has recorded it in the Oxford Clay, and Mr. Leckenby in the 

 Kelloway Hock and Calcareous Grit of Yorkshire, M. Quenstedt quotes it from the 

 Cornbrash of Wurtemburg ; M. Agassiz from the Oxfordian Strata of the Vadois Jura and 

 the Jura of Soleure. 



Pholadomya ovulum, Ag. Tab. XXXV, figs. 18, 18 «. 



Pholadomya ovulum, Ag. 6t. Crit. Myes., p. 119, tab. 3, figs. 7 — 9; tab. 3 h, 



figs. 1—6. 



— — D'Orb. Prodr., 11 et., No. 168, vol. 1. 



— — Morris. Catal. Brit. Foss., 1854, p. 221. 



— — Oppel. Juraformation, p. 481. 



Testa ovato-elongata, antice breviore, rotundata, cordata, posterius producta, attenuata, 

 margine inferiore arcuate curvato, superiore subkorizontali, concavo, umbonibis crassis 

 subanticis prominulis ; valvis concentrice plicatis, plicis longitudinalibus numerosis incB- 

 qualibus mediocriter tenuibus ; costellis radiantibus obliquis cequalibus angustis, inferne 

 evanescentibus, apertura postico et antico angusto. 



Shell ovately elongated; the anterior side short, rounded, cordiform ; the posterior side 

 produced and attenuated; the inferior margin is curved elliptically ; the superior margin is 

 moderately lengthened and concave ; the umbones are elevated and tumid ; the sides of 

 the valves are convex, with closely arranged but not prominent longitudinal plications ; 

 the radiating costa3 are very narrow or linear, disposed obliquely, about twelve in number; 



