IGO DIMYARIA. 



Genus 56.— LUTRARIA Lamarck. 



Generic Character. — Inequilateral, transversely oblong, 

 or rounded, gaping at the extremities; hinge with one tooth, 

 which is somewhat complicated, or two teeth, of which one 

 is simple, with an adjoining deltoid hollow, which is oblique, 

 and projecting internally J no lateral teeth; ligament inter- 

 nal, attached in a pit. 



The want of lateral teeth, at once distinguishes the shells of this 

 genus fi'om those of Mactra. 



Lutraria elUptica.—Tms. Oval Lutraria. Plate XVIII. 

 fig. 4. Oblong-oval, nearly smooth, having a few concen- 

 tric, nearly obsolete wrinkles; and some diagonal striae at 

 the ends of the valves; of a fine yellow, or greenish-brown; 

 inside white. Five inches broad. Inhabits the seas of 

 Europe. 



There are two sections in this genus.—* Shell transversely oblong. 

 #* SheU orbicular. 



Section IV. — Crassipedes. — The mouth united in 

 front, or partly so; foot thick, posterior; shell gaping when 

 closed. 



TRIBE I. MY ARIA. 



Shells having a broad spoon-like tooth in each valve, or 

 in one only; gaping at both extremities, or only at one end. 



Genus 57.— ANATINA Lamarck. 



Generic Character Transverse, subequivalve, gaping at 



both sides, or at one only ; no cardinal teeth ; one broad 

 primary tooth in both valves, projecting interiorly; a lateral 

 plate or rib running obliquely under the primary teeth. 



Sometimes there is a fissure or suture extending from the apex, 

 giving the appearance of a second plate or rib. 



These shells form a connecting link between the Mactrse and Myse. 



