LED A. 165 



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

 They were so described in the British MoUiisca by Forbes and Han- 

 ley. I think there is good reason to follow the subsequent deter- 

 mination of Mr. Hanley as given in Sowerby's Thesaurus, and des- 

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

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

 responds with specimens sent me under this name by McAndrew 

 and Mcirch. It is distinguished by its swollen and abbreviated form, 

 pouched ventral margin, and dark epidermis. The younger ones 

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



Leda caudata. 



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

 laleate ; beaks acute ; epidermis wax yellow, concentrically furrowed. 



Area minuta, Moxtagu, Test. Brit. 140; id. Chcnu ed. 61. 



Area eaudata, Donovan, Br. Sh. pi. 78 ; id. Chcnu ed. 50, pi. 17, figs. 8-12. 



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



Nucula rostrata, Sowerby, Gen. fin'. 5. — McGilliv. JIgU. Aberd. 245. 



LembuJus sulcatus, Leach, Moll. Brit. pi. 12, figs. .3, 4. 



Leda caudata, Lovex, 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). — Alder, Cat. Moll. Nortluimb. 79. 



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



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

 intermediate between L. tenuisulcata and L. minuta. Compared 

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

 the Ijeaks 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 o))esity, its 



much longer rostrum and its wax yellow epidermis. 



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



breadth, 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 UNIONID^E. 



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

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

 destitute of teeth ; muscular impressions compound. 



