142 PROCEEDINGS OP THE ACADEMY OF 



Species, being ovate in form instead of globose-cordate. It also differs in 

 having greatly less elevated beaks. 



We dedicate the species to Mr. W. Stimpson, Naturalist of the South Pacific 

 Exploring Expedition, to whom we are under obligations for suggestions re- 

 specting this and the preceding species. 



Locality and position. Same as last. 



Pholadomya subventricosa. 



Shell longitudinally oval, ventricose in the umbonial and buccal regions, 

 more compressed behind ; extremities rounded ; base forming an elliptic curve ; 

 dorsum concave behind the beaks, declining very abruptly in front ; beaks ele- 

 vated, gibbous, located near the anterior end, distinctly incurved ; surface orna- 

 mented by about thirty very small, rather flexuous, radiating costae, some of 

 which die out before reaching the beaks, crossed by faint concentric wrinkles, 

 and fine rather indistinct lines of growth, which produce on the costse very 

 small irregular nodes or granules ; costse most distant near the extremities of 

 the shell, and wanting on an oval or cordate space at the anterior end. Length 

 about 2 inches ; height 1.10 inch ; breadth 1-10 inch. 



This shell resembles very nearly a Lower Green sand species described by 

 Prof. Forbes in the Journ. Geol. Soc. Lond. vol. i. p. 238, pi. 2, fig. 3, under the 

 name of P. Martini; but the beaks are more elevated, and nearer terminal in 

 our shell, and the costae more numerous. The concentric wrinkles likewise 

 differ in being not quite so distinct as on P. llariini. 



It is yet more closely allied to a species described by one of the writers* in 

 Trans, Albany Institute, vol. 4, p. 42, from Vancouver's Island, under the name 

 of P. subelongata ; but has more elevated beaks, and finer, as well as more 

 numerous costfe ; the buccal end is also more gibbous than in P. subelongata. 



Locality and position. Mouth of Judith River, formation No. 1 ? of general 

 section. 



SOLEN? DaKOTENSIS. 



Shell long and slender, rather compressed ; dorsal margin and base parallel : 

 posterior end narrowly rounded, (anterior end?); beaks not distinct from the 

 dorsal edge, located near the centre of the shell; surface of cast marked by very 

 obscure traces of concentric wrinkles, indicating the direction of lines of 

 growth. Length 1.40 inch; height .35 inch; breadth about .20 inch. 



This species resembles S. cequalis, D'Orbigny, (Pal. Franc, tom. 3d, pi. 350, 

 figs. 5, 6,) more than any shell with which we are acquainted ; but is propor- 

 tionally narrower, and the beaks are less distinct from the cardinal border. 

 The only specimen we have seen is a cast of the outside of both valves, lyi"g 

 partly open and embedded in the matrix. Although we know nothing of rLe 

 surface markings or interior of this shell, we have ventured to characterize it, 

 believing it important to call attention to the few forms found in the formation 

 in which it occurs, however obscure they may be, as there remains some doubt 

 in regard to the exact age of this deposit. 



Locality and position. Just below the mouth of Vermilion River on the Mis- 

 souri, formation No. 1 of general section. 



New Gen. CORBULAMELLA. 



The small shell upon which we propose to establish the above genus appears 

 to be related both to Cardilia of Deshays, and Corbula of Bruguiere. It differs 

 from the first, however, in being distinctly inequivalve, and in wanting the 

 spoon-shaped projection for the reception of the ligament, mentioned by 

 Deshays. From Corbula it differs in having the posterior muscular attacliment 

 raised upon a thin, strongly projecting plate, as in Cuculloea. The teeth of the 

 hinge, and pallial impression appear to be as in Corbula. We have not been 

 able to determine whether the ligament was internal or external. 



* Mr. Meek. 



[May, 



