46 INVERTEBRATA OF MASSACHUSETTS. 



In the course of the reformations recently made in the in- 

 definite genus Anatina of Lamarck, this natural group of shells 

 has received several generic appellations. A genus was instituted 

 by Leach, to receive the old Mya JVorvegica, which he called 

 Magdala ; and, still later, Scacchi has named it Pandorina. 

 Perhaps I may be censured for breaking, in this instance, the 

 salutary rule, that the oldest published name should take prece- 

 dence of all others. The genus Lyonsia of Turton certainly 

 preceded that of Osteodesma, and so, I think, did Magdala. 

 But the name Osteodesma is so well chosen, and is so well 

 made known in the recent edition of Lamarck's work, being, 

 moreover, the type of the natural family Osteodesmacea, that I 

 cannot refrain from giving it the preference. 



Osteodesma hyali'na. 



Shell sub-ovate, fragile, pearly, translucent, inequilateral ; elon- 

 gated, compressed and truncated posteriorly ; covered with radiating 

 wrinkles ; ossiculum a truncated wedge. 



Figure 10. ^^■ 



State Coll., No. 220. Soc. Cab., No. 250. 



Mya hyalina, Conrad ; Journ. Acad. Nat. Sc, vi. 261, pi. 11, f. 12. 

 Lyonsia hyalina, Conrap ; Amer. Mar. Conch., 51, pi. 11, f. 2. 

 Osteodesma hyalina, Couthouy ; Bost. Journ. JVat. Hist., ii. 166. 



Shell elongated, subovate, thin, fragile, pearly, translucent, in- 

 equilateral, the posterior side much the longest, narrowed, closely 

 compressed at the end, but slightly truncated, so as to gape a 

 little ; posterior superior margin a straight Hne, and compressed ; 

 the remaining outline regularly rounded ; beaks prominent, inclin- 

 ing forwards ; region of the beaks tumid and smooth ; a broad 

 marginal portion is covered with a thin membranous epidermis 

 projecting beyond the edge, and wrought into regular wrinkles, 

 radiating from the beaks ; these wrinkles are minutely fringed so 

 as to entangle grains of sand, by which the surface is sometimes 

 entirely coated. The hinge consists of a delicate ledge, running 

 from the beak obliquely downward and backward, serving for the 

 attachment of a ligament, which is also attached to the edge of 

 the wedge-shaped ossiculum lying against that part. Muscular and 



