MACTRA. 77 



localities ; but I appreliciul that 31. falcata, Gould, is the species 

 referred to. 



This shell is inferior in size to the M. soKdissimn only. The 

 largest valve I have seen measures four and one fifth by two and 

 four fifths inches. In general it is found smaller than the dimen- 

 sions given. Such specimens have a straw-colored epidermis. 



Its size, shape, and surface distinguish it from M. g-randis, 

 Chemn., 31. soUda, and all other known species except 31. so/idis- 

 sima. Compared with that more common shell, it differs in its 

 coarser surface, its thick, dusky epidermis, its less elevated beaks 

 and less convex valves, the longer and less elevated anterior por- 

 tions, the rough, oval portion behind the beaks embracing more 

 of the shell, the more feeble hinge, the stout and firm V tooth, 

 and the deep sinus of the pallial impression. 



I have very little douljt that this is the shell described by De- 

 shayes as 31. g-randis. The description corresponds well. But, 

 as it is not figured or quoted by other authors, and the hal^itat 

 was not known to him, it is impossible to decide with certainty. 

 Singularly enough too, Deshayes himself does not cite it in his 

 new edition of Lamarck. Provided it be the same, however, the 

 specific name must necessarily be changed, as his name was pre- 

 viously given to a different species by Chemnitz. 



This appears to be the same species, a small specimen of which 

 is figured by Mr. Gray in the Appendix to Beechey's Voyage, 

 under the name of 31. siiniUs. This name is preoccupied Ijy Mr. 

 Say. 



It is objected that the name ovcdis has been used for a fossil 

 species ; Ijut if the generic term Spisula be adopted, this shell will 

 retain the above name. As before ol^served, Philippi's pondcrosa 

 appears to me to represent a variety of M. solidissima, rather than 

 this species. 



Mactra lateralis. 



Figs. 34, 35. 



Shell small, triangular, very convex, nearly eqnipartite; beaks elevated, the 

 spaces before and behind them broad heart-shaped. 



Mactra lateralis, Say, Jonrn. Ac. Nat. Sc. ii. 309. — Coxrad, Amer. Mnr. Conch. 62, 

 pi. 14, fig. 4. — De Kay, Nat. Hist. New York, 230, pi. 29, fig. 287. — Philippi, 

 Abbild. pi. 1, fig. 3. 



Shell small, triangular, tumid, nearly smooth, shining ; nearly 

 eqnipartite, the posterior part somewhat prolonged, and sloping 



