MACTRACEA. MOLL CISC A. MACTRA. 53 



ply a variety of M. solidissima or not, I will not presume to decide from 

 this one specimen; and, as it is not strictly a Massachusetts shell, I 

 shall merely notice it in this way. The shell has certainly 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 If inch, height 1/^ inch, breadth f inch. 

 M. similis, length l^ inch, height lj\, inch, breadth f inch. 



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

 Dr. Loven of Stockholm, which he calls M. luteola. I cannot per- 

 ceive that it differs from the young of tliis shell, of a corresponding 

 size. 



Mactra ova' lis. 



Bhell Inrge^ thick, ohovate^ coarse, nearly equilateral, covered 

 with a tough, dusky-broicn ejndermis ; V tooth strong ; lateral teeth 

 not striated ; sinus of palleal impression deep. 



Figure 32. 



State Coll., No. 229. Soc. Cab., 2324. 



JVJactra siniilis, Grav; Jlppend. to Bcechcy's Voyage, pi. 44, f. 8. 

 Mactra grandis, Deshayes ; Encyc. M6th., Vers, ii. 305, not M. grandis of Chem- 

 nitz and others. 



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

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

 hinge margin Being slightly concave, it is there somewhat narrow- 

 ed ; posterior slope convex, extremity slightly gaping, base regu- 

 larly curved ; beaks but little elevated ; before, there is a short, 

 faintly defined areola ; behind them is another portion bounded by 

 an elevated line extending from the beaks to near the lower angle, 

 and here the epidermis is very coarsely and loosely wrinkled ; 

 the surface has a rugged appearance from the coarse lines of 

 growth, and is rendered still more so by the folds of the thick, 

 strong, dusky-brown epidermis in the same direction. Interior 

 bluish-white ; hinge supports strong and smoothly rounded ; V 

 tooth strong and firm, having the anterior side in the right valve 

 much more elevated than the posterior ; lateral teeth short and 

 slender, not striated ; muscular and palleal impressions rather 

 superficial ; sinus of the latter deep. Length 3i inches, height 

 2\ inches, breadth li inch. 



