BIVALVIA. 271 



PANDORA OBTUSA. Desk. 2d ed. Lamarck, torn, vi, p. 145, No. 2. 



G. B. Sowerly. Spec. Conch. (Pand.), p. 2, figs. 13. 



Phil. En. MoU. Sic., vol. ii, p. 14, t. 13, fig. 13. 



Forb. SLuAHanl. Hist. Brit. Moll,, vol. i, p. 210, pi. 8, fig. 5; and 



pi. G, fig. 10, animal. 

 TRUTINA SOLENOIDEA. Brown. Illust. Brit. Couch., pi. 13, fig. 5, 1827. 



Spec. Char. Testa obtme-elongatd; later e postico versus extremitatem dilatato; margine 

 dor soli planiusculo. 



Shell obtusely elongate ; posterior side dilated towards the extremity; dorsal margin 

 nearly straight. 



Length, -f inch. Height, f inch. 



Locality. Red Crag, Walton Naze. 



Only two or three specimens of this species have fallen under my observation, and 

 I have, in deference to the malacologists, separated this from what is called rostrata. 

 Colonel Montague, who, notwithstanding his having described the two shells under 

 different generic names, was afterwards of opinion that the one was only the younger 

 state of the other. Messrs. Forbes and Hanley consider the characters of the animal, 

 as well as those of the shell, to be quite distinct, and have kept the two forms 

 separate. My own specimens are not sufficiently numerous or perfect to assist in 

 the determination. The two shells are so much alike in the young state as to be with 

 difficulty determinable ; and I am inclined to believe with Montague, so far at least in 

 their specific identity, that if the one be not exactly the young state of the other, there 

 is not more than a local variation between the two. Both appear to have existed 

 during the Crag Periods, the rostrata in the Cor. Crag corresponding with the more 

 Southern form, while that from the Red Crag resembles the Northern one (probably 

 P.glacialis, Leach, 'An. Phil.,' vol. xiv, p. 203, 1819). 



,* J. E. Gray, 1830. 



ANATINA (sp.) Lamk. 

 CORBULA (sp.) Desk. 1835. 

 THRACIA (sp.) Brown, 1827. 



ERYCINA (sp.) Risso, 1826. 

 CUSPIDARIA. Nardo, 1840. 



Generic Character. " Shell transversely ovato-pyriform, inequivalve, inequilateral, 

 more or less beaked, and gaping posteriorly ; surface smooth or striated, or ribbed 

 longitudinally, never punctated, with or without an epidermis ; valves strengthened 

 internally with a longitudinal rib ; hinge composed of a cartilage fulcrum, usually 

 oblique, and spatulate in each valve, sometimes with a minute tooth beside it, and a 

 more or less developed lateral tooth on the rostral side of one or both valves ; ligament 

 external (?), small ; muscular impressions large, pallial with a very shallow sinus. 



* Etym. (?) Necupa, proper name. This is also employed for a genus of insects. 



