MACTRA. 75 



at Newport, I presume to be the M. similis of Say. Whether it be 

 simply a variety of M. solidissima or not, I will not presume to de- 

 cide from this one specimen ; and as it is not strictly a Massachu- 

 setts shell, I shall merely notice it in this way. The shell has cer- 

 tainly quite a different aspect. It is triangular, the beaks are more 

 elevated, the marginal outlines are straight, and the comparative 

 dimensions vary as follows : — 



M. solidissima, length, one and four fifths inches; height, one 

 and three twentieths inches ; breadth, three fifths of an inch. 



M. similis, length, one and four fifths inches; height one and 

 four tenths inches ; breadth, four fifths of an inch. 



[No doubt is now entertained of their distinctness.] 



M. ponderosa of Philippi I should regard as a form of this spe- 

 cies and not of the following. 



Dr. Stimpson found in abundance a most extraordinary form, 

 short and ventricose, but with the striated teeth and general char- 

 acters of the species. Its relative dimensions were, length, three 

 and one eighth inches ; height, two and one half inches ; breadth, 

 one and one half inches ; and these proportions are maintained 

 through the very young specimens. It inhabits Grand Manan, and 

 may be called var. curta. 



Our species all belong to that subdivision of the old Linnean 

 genus which Dr. Gray calls Spisula. 



I have received a shell, about three fourths of an inch long, 

 from Dr. Loven of Stockholm, which he calls M. liiteola. I can- 

 not perceive that it differs from the young of this shell, of a cor- 

 responding size. 



Mactra ovalis. 



Fig. 32. 



Shell large, thick, obovate, coarse, nearly eqnipartite, covered with a tough, 

 dusky-brown eiaidermis; V tooth strong; lateral teeth not striated; sinus of pal- 

 lia! impression deep. 



3f(ictra similis, Gray, Append, to Bccchcy's Voyage, pi. 44, fig. 8. 



Macira c/ra,idis, Deshayes, Eiicyc. Meth. Vers, ii. 395, not M. grandis of Che.mxitz and 



others. — Mighels, Jonrn. Bost. Soc. Nat. Hi,-<t. iv. 316. 

 Mactra ovalis, Gould, Inv. Mass. 1st ed. 53. — De Kay, Nat. Hist. New York, 230.— 



MiDDENDORFF, Sibcr. Reise (Moll.) 103. — Keeve, Couch. Icon. tig. 36. 

 Macira ponderosa, Stimpsos, Shells of New England, 20. 

 Mactra pohjnijma, Stimpson, Check List, East Coast Sliells, 3. 



Shell large, thick and coarse, somewhat compressed, sub-oval, a 

 little shortest anterior to the beaks, and, the anterior slope of the 



