LYONSIA. 



63 



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

 fdamcnts or soft spicula. 



Found about the sandy regions of Cape Cod, and not unfre- 

 quently discovered adiiering to oysters in tlie market. Dr. J. AV. 

 Migheis of Portland, Maine, has taken it by dredging in Casco 

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

 in four fathoms; Eastport, five fathoms; Marl)lehead {Haskcl/); 

 Grand Manan {Sfiiiipsoii) ; Salem Ihirhor {W/i cat land) ; Nantucket 

 {P(u-ker) ; Vineyard Sound (Ag-assiz) ; Buzzard's Bay {Prime 

 and Stimpson) ; Sable Island (Willis). 



This is a very curious shell, easily recognized liy Its pearly sub- 

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

 species yet described it is distinguished by the two lines l)order- 

 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 the 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 

 shell. 



Family ANATINID^. 



Shkll elongated, inequipartite, inequivalve, fragile, somewliat 

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

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

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

 foot slender, l»rancliia3 with a single leaf, siphons long, separate, 

 fringed. 



There seems a propriety in separating from the family Myadce 

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

 pearly ilil)ric of the sludl, and the presence of the little irregularly 

 shaped 1jone resthig against the hinge within, are well-marked 

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

 in the sand about low-water mark. 



Gcmi»» I.Y01VSIA, Turton. 1S22. 



Shell inequivalve, su1)triangular, fragile, pearly ; hinge having a 

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

 and against which adheres a four-sided ossiculum. 



