64 anatinidj:. 



In the course of the reformations recently made in the indefinite 

 genus Anatina of Lamarck, this shell has passed under several ge- 

 neric appellations. A genus was instituted by Leach, to receive the 

 old 3I//a JVorvegica, which he called Mag-dala, and, still later, Scac- 

 chi has named it Paridorim. Perhaps I may be censured for 

 In-eaking, in this instance, the salutary rule, that the oldest pub- 

 lit-hcd name should take precedence of all others. The genus Ly- 

 onsia certainly preceded that of Osteodesma, and so, I think, did 

 M(vdala. 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 Octeodesmacea, that I can- 

 not refrain from giving it the preference. [More mature considera- 

 tion has induced me to conform to the general consent of conchol- 

 ogists and adopt the older name. Mag-dala was only a manuscript 

 name until 1827. 



Lyonsia hyalina. 



Fig. 31. 



Shell sub-ovate, fragile, pearly, translucent, inequipartite ; elongated, com- 

 pressed, and truncated posteriorly; covered Avith radiating wrinkles; ossiculum a 

 truncated wedge. 



Mija hjnJina, Conrad, Journ. Acad. Nat. Sc. vi. 2G1, pi. 11, fig. 12. 



Lyonsia hijulma, Conrad, Amer. Marine Conch. 51, pi. 11. fig. 2. — Stimpson, Shells of 



New England, 23 ; Inv. Gr. Manan, 21. 

 Osteodesma hyalina, CouTHOUY, Best. Journ. Nat. Hist. ii. 166. — De Kay, Nat. Hist. 



New York, 234, pi. 33, figs. 311, A, B. — Gould, Inv. Mass. 1st ed. 46.— 



MiGHELS. Bost. Journ. Nat. Hist. iv. 315. 



Shell elongated, sub-ovate, thin, fragile, pearly, translucent, in- 

 equipartite, the posterior part much the longer, nar- 

 Fig. 380. rowed, closely compressed at the end, but slightly 



truncated, so as to gape a little ; hinge margin a 

 straight line and compressed ; the remaining out- 

 L. hyalina. l^^^ rcgiilarly rounded ; beaks prominent, inclining 



forwards ; region of the beaks tumid and smooth ; 

 a broad marginal portion is covered by a thin membranous epider- 

 mis projecting beyond the edge, and wrought into regular wrin- 

 kles, 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 



