LEDA. 165 



of regarding two very distinct forms as varieties of the same species. 

 They were so described in the British j\Iollusca by Forbes and Han- 

 ley. I tliink there is good reason to follow the subseqnent deter- 

 mination of Mr. Hanley as given in h>owerl)y's Thesanrns, and des- 

 ignate two species. This form is the more northern one, -which 

 I had not seen when the former edition was puljlished. It cor- 

 responds with si)ecimens sent me nnder this name by McAndrew 

 and Morch. It is distingnishcd by its swollen and al)breviated form, 

 ponched ventral margin, and dark epidermis. The younger ones 

 (var. complanata) are more compressed and longer beaked. 



Leda caudata. 



Long and slender, compressed, gradually tapering backwards, and decidedly 

 falcate ; Ijcaks acute ; epidermis wax yellow, concentrically furrowed. 



Area minula, Montagu, Test. Brit. 140; id. Cliemi cd. 01. 



Area caudata, Donovan, Br. Hli. pi. 78 ; id. Clicuu cd. 50, pi. 17, figs. 8- 12. 



Nitcula minula, Turton, Brit Blv. 178. — Hanley, Recent Shells, i. 168, pi. 10, fig. 44. 



Nncula roslruta, Sowerby, Gen. fig. .■). — .McGilliv. Moll. Aherd. 245. 



Lenihiilus sidcutus, Leacif, Moll. Brit. pi. 12, figs. 3, 4. 



Leda caudata, Lov^n, Ind. Moll. Scand. 34. — Forbes and Hanl. Br. Moll. ii. 226, pi. 

 47, figs. 11-13; pi. P. fig. 2 (animal). — Hanley, in Thes. Conch, iii 114, pi. 228, 

 fig. 60. — Gray, Cat. Br. Moll. 66 (part). — Aluer, Cat. Moll. Northnmb. 79. 



Leda complanata, Moller, Ind. Moll. Grccnl. 17. 



Perhaps the best way to delineate this species is to say that it is 

 intermediate between L. tenuisulcata and L. miiiuta. Compared 

 with L. tenuisulcata, which it most resembles, it is much smaller ; 

 the beaks are more acute, the umbonal region less tu- 

 mid, the posterior portion more recurved, being quite 

 falcate in consequence of concave outline of the dorsal 

 margin, while that of L. tenuisulcata is nearly direct. 

 From L. minuta it differs in its want of obesity, its 

 much longer rostrum and its wax yellow epidermis. 

 Length, three hfths of an inch ; height, one fourth of an inch ; 

 l)rcadth, three twentieths of an inch. 



The only specimens I have seen were received from Mr. Willis of 

 Halifax ; Greenland (March and Moller). It is a more southern 

 form than L. minuta. 



Family UNIONIDyE. 



Shells fluviatile; liinge having a simple or divided, furrowed, car- 

 dinal tooth, with or without a long marginal tooth ; and sometimes 

 destitute of teeth ; muscular impressions compound. 



