LYONSIA. 63 



per one smallest, diverging at their orifices, wliieli are fringed with 

 filaments or soft spicula. 



Fonnd abont the sandy regions of Cape Cod, and not unfre- 

 quently discovered adhering to oysters in the market. Dr. J. W. 

 Mighels of Portland, Maine, has taken it l)y dredging in Casco 

 Bay. Mr. Say found it as far south as Florida. Boston Harbor 

 in four fathoms; Eastport, five fathoms; Marblehead {Haske/l); 

 Grand Manan ( Stiuipson) ; Salem Harbor ( Wheatland) ; Nantucket 

 {Parker) ; Vineyard Sound (^As^assiz) ; Buzzard's Bay (^Prime 

 and Sfimpson) ; Sable Island {Wi/lis). 



This is a very curious shell, easily recognized by its pearly sub- 

 stance, its flat valve, and its upward curved tip. From all other 

 species yet described it is distinguished by the two lines border- 

 ing its posterior hinge margin. Mr. Say has figured a small young 

 specimen ; the rostrated tip is represented as too slender, as is 

 also the whole shell, and the pouch-like appearance of tlie poste- 

 rior base is not sufficiently indicated for adult shells. There is 

 often a good deal of contortion and irregularity in the shape of the 

 ^hell. 



Family ANATINID.^. 



Shell elongated, inequipartite, inequivalve, fragile, somewhat 

 pearly, slightly gaping at one end ; hinge with a thickening or 

 spoon-shaped process, to Avhich the ligament is attached, usually 

 supported within by an ossiculum. Animal with the mantle closed, 

 foot slender, branchiae with a single leaf, siphons long, separate, 

 fringed. 



There seems a propriety in separating from the family Myadae 

 some of the genera formerly included under it. The delicate and 

 pearly fabric of the shell, and the presence of the little irregularly 

 shaped bone resthig against the hinge within, are well-marked 

 characters. These shells attain to a considerable cize, and live 

 in the sand about low-water marlt. 



Oemts LYO:V.SIA, Turtox. 1822. 



Shell inequivalve, subtriangular, fragile, pearly ; hinge having a 

 narrow ledge within each valve, to which the ligament is attached 

 and against which adheres a four-sided ossiculum. 



