LEDA. 165 



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

 They were so described in tlie British MoUusca l)y 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 Ibrm is the more northern one, which 

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

 responds with specimens sent me under this name by McAndrew 

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

 pouched ventral margin, and dark epidermis. The younger ones 

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



Leda caudata. 



Long and slender, eompressed, gradually tapering l3ackwards, and decidedly 

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



Area nu'mita, Montagu, Test. Crit. 140; id. Ciieiiu od. (H. 



Area eaudata, Donovax, Br. Sh. pi. 78 ; id. Chenu ed. 50, pi. 17, tigs. 8-12. 



Nucida minuta, Turton, Brit. Biv. 178. — H.vnley, Recent fShcIls, i. 168, pi. 10, tig. 44. 



Nucula rostruta, Sowerby, Gen. fig. 5. — McGilliv. ^loll. Aberd. 24.5. 



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



Leda caudata, Loven, Ind. Moll. Seand. 34. — Forbes and Hanl. Br. Moll. ii. 226, pi. 

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

 fig. 60. — Gray, Cat. Br. Moll. 00 (part). — Alder, Cat. Moll. Northumb. 79. 



Leda complanata, Moller, Ind. ;\Ioll. Grocid. 17. 



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

 intermediate between L. teriuisulcata and L. minuta. Compared 

 with L. teriuisulcata^ which it most reseml)les, it is much smaller ; 

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



, . Fig- 471. 



mid, the posterior portion more recurved, being quite 

 falcate in consequence of concave outline of the dorsal 

 margin, while that of L. temnsulcata is nearly direct. 0^' 

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



. . , . L. caudata. 



much longer rostrum and its wax yellow epidermis. 



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



l)readth, three twentieths of an inch. 



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

 Halifax ; Greenland (Md'rch and Moller^. It is a more southern 

 form than L. minuta. 



Family UNIONID^. 



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

 dinal tooth, with or witliout a long marginal tooth ; and sometimes 

 destitute of teetli ; muscular iinprossioiis compound. 



