132 AMERICAN MARINE CONCHOLOOY. 



Genus XYLOTRYA, Leach. 

 Menke, Syn. Meth. 1830. 



1. X. fimbriata, Jeffreys. Figs. 295-297. 

 Ann. and Mag. Nat. Hist., 3d ser. vi. 126. 

 Shell subtrigonal, diameters about equal, striae on anterior area 

 about thirty ; posterior auricle large, sloping from the beak and 

 descending much below the anterior triangle, inner face fan- 

 shaped, large, overhanging, concave, "concentrically striate. Pal- 

 lets oar-shaped, the blade as long as the handle. 

 Diam. 6 mill. Pallets 12 -+- mill. long. 



New Bedford, Mass., Fort Macon, N. O. 



The valves resemble those of T. naoalis so closely that they 

 are scarcely distinguishable from that species. The pallets are, 

 however, entirely different. 



Family ANATINID.E. 



Shell thin, generally inequivalve ; interior nacreous ; external 

 surface granular; ligament external, thin; cartilage internal, 

 placed in opposite pits and furnished with a free ossicle ; muscu- 

 lar impressions faint, the anterior elongated ; pallial line usually 

 sinuated. 



Animal with mantle-margins united ; siphons long, more or less 

 united, fringed; gills single on each side, the outer lamina pro- 

 longed dorsally beyond the line of attachment. 



Synopsis of Genera. 



Oval ; inequivalve, left valve deepest ; posterior side very short and con- 

 tracted; beaks fissured, strengthened within by oblique diverging ribs; 

 hinge with a spoon-shaped process in each valve containing the cartilage 

 and ossicle. Periploma, Schum. 



Subtriangular ; inequivalve, fragile ; hinge having a narrow ledge within 

 each valve, to which is attached the ligament and an adhering four-sided 

 ossiculum. Lyonsia, Turton. 



Oblong; nearly equivalve, slightly compressed, attenuated, and gaping 

 posteriorly, smooth or minutely scabrous ; cartilage processes thick, not 

 prominent, with a crescentic ossicle. Thracia, Leach. 



Inequivalve, transverse, thin ; valves close, attenuated behind ; right valve 

 flat, with a diverging ridge and cartilage furrows ; left valve convex, 

 with two diverging grooves at the hinge. Pandora, Brug. 



