132 AMERICAN MARINE CONCIIOLOaY. 



Genus XYLOTRYA, Leach. 

 Menke, Syii. Melh. 1830. 



1. X. PiMBRiATA, Jeffreys. Figs. 295-297. • 

 Ann. and Mag. Nat. Hist., Bd scr. vi. 126. 

 Shell subtrigonal, diameters about equal, stri.ie 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, concentricali}^ striate. Pal- 

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

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



Nero Bedford^ Mass., Fort Macon., N. C. 



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

 are scarcely distinguishable from that species. Tiie pallets are, 

 however, entirely different. 



Family ANATINID.^. 



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 ; pallia! 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.. 



8ynoj)sis of Genera. 



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

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

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

 and ossicle. Peuiploma, Sclium. 



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 cquivalve, sliglitly compressed, attenuated, and gaping 

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

 prominent, with a crescentic ossicle. Tuuacia, 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. 



