Fam. 26.] NATITRAL HISTOIIY SOCIETY. 107 



Order ANOMALODESMACEA. 



Hinge imperfect, often without teeth, ligament, or cartilage, 

 frequent!}^ strengthened by extra valves ; substance of shell often 

 hard and brittle; sometimes with pearly layers. 



Family 25. ANATINID/E. 

 Shell oval to oblong, more or less inequivalve, closed or gap- 

 ing slightly at one end ; both external ligament and internal 

 cartilage ; pallial line obscure. 



* Ends of shell quite different; 2 gonial ridges /. Thracia. 



* Ends much alike; no distinet gonial ridges 2. Pen'ploma. 



1. Thracia, Blainv. 



Shell inequivalve, gaping at the narrow posterior end. 



Animal siphons rather long, with separated, fringed orifices. 



1. Tkracia Conradi, Cout. Shell ovate-orbicular, rounded be- 

 fore, narrowed and truncated behind, thin, fragile and slightly 

 gaping ; right valve larger and much more convex than the left ; 

 two gonial wave-like ridges extend to the sides of the truncated 

 end ; ligament large, rounded ; pallial impressions broad and 

 deep ; sinus acute. Exterior ashy, interior chalky-white, pearly 

 between ; epidermis, when seen, brownish. 1^. 75; H. 65 ; W. 38 ; 

 U. ^; sometimes larger. — New England. Rare. 

 2, Feriploma, Schum. 



Shell oval, very inequivalve, slightly pearly; internal cartilage 

 in spoon-shaped pits. 



Animal siphons long, slender and divided throughout. 



1. Periplom.a (^Cochlodcwid) Lennv.m^ Con. Shell sub-oval, very 

 thin, brittle and slightly gaping; the right valve convex nnd 

 somewhat truncated behind ; the left valve nearly flat and 

 rounded at both ends ; a spoon-shaped process extends down- 

 ward and a little backward from the umbo in each valve for in- 

 ternal cartilage; surface wrinkled. White, with a thin yellowish 

 epidermis. L. 35; H. 24; W. 11 ; U. J.— Whole coast. Com- 

 mon in 3-10 fathoms ; dead shells thrown upon the beach by 

 storms. 



Family 26. LYONSIID/€. 



Shell nearly equivalve, left valve the larger, thin, nearly or 

 quite closed; pallial line obscure, the sinus angular. 



