MACTRACEA. MOLLUSCA. MACTRA. 51 



of our shells by its toothless hinge ; and, when the valves happen to be 

 found united, the disparity in their size and convexity is at once per- 

 ceived. When the external coating is removed, we come to a silvery 

 substance like mother-of-pearl. I have a specimen, the dimensions of 

 which are, length 4 inches, height 3^ inches, breadth 2 7 V inches. 

 Dr. Prescott of Lynn has one nearly as large. 



I have carefully dissected the animal, and find it to correspond in all 

 essential particulars with the anatomy as laid down in Kiener. 



Like many others of our shells, this has had the misfortune to have 

 several names applied to it which it cannot claim. It is beautifully 

 and accurately figured by Mr. Conrad, but his synonymy is entirely 

 erroneous. In the "Catalogue of Animals and Plants of Massachu- 

 setts, 1834," it is referred to under the name of Anatlna convexa. In 

 Dr. Store r's Translation of Kiener's " Iconography," &c., it is alluded 

 to under the supposition that it is T. corluloides, to which species it 

 is, indeed, closely allied. But it is more equilateral, more rounded, 

 proportionally narrower behind, and its surface has not the shagreen 

 roughness of that shell. 



Mr. Couthouy has fully pointed out its distinctive characters, and es- 

 tablished it as a species ; and for more minute particulars his article in 

 the " Boston Journal " may be referred to. 



FAMILY MACTRACEA, LAM. 



Shell equivalve, usually somewhat gaping at sides ; hinge with an internal 

 cartilage, and sometimes an external ligament also. 



GENUS MACTRA, DESK. 



Shell transverse, slightly -gaping at sides; beaks prominent; 

 hinge a prostrate, concave tooth to contain the cartilage, having at 

 one margin a delicate, erect tooth like the letter V ; two lateral 

 teeth near the central ones. 



MACTRA SOLIDISSIMA. 



Shell large, massive, strong, oval, covered with a dirty-brown 

 'epidermis, sub-equilateral; hinge strong, V tooth delicate ; palleal 

 impressions slightly indented posteriorly. 



State Coll., No. 228. Soc. Cab., No. 1729. 



Mactra solidissima ; CHEMN. ; Conch., x. 1. 170, f. 1656. DILLWYN ; CataL, i. 140. 

 WOOD; Index, pi. 6, f. 22. CONRAD ; Amer. Mar. Conch., 64, pi. 14, f. 7. 



