OF CONCHOLOGY. 143 



ens the probability that he referred to Propilidium (Forbes and 

 Hani.), which is figured by them also without them ; and their 

 figure has been copied by Adams and others as Lepeta cceca. But 

 these appendages are present, and even conspicuous, in specimens 

 from Grand Menan in the Smithsonian Cabinet, and also were 

 perceptible in Prof. Sar's dry specimen, from which the ribbon was 

 obtained ; they are also present in the two species of Crypto- 

 branckia from the Pacific and Behring Strait. Hence it is hardly 

 probable that they could have been overlooked. 



Subgenus Cryptobranchia, Dall ex Midd. 



Syn. Cryptohranclaa^ Midd. (pars). Sib. Reise, p. 183. Idem, 

 Schrenck (pars), Reise von Amurl. Moll. p. 291. 

 Lepeta, Carpenter, Suppl. Rep. pp. 603 and 651 (not 

 Gray). 



Diag. Apex inch anteriorly ; shell slightly or not colored, 

 striated. Rhachidian tooth provided with three nearly 

 equal denticles. Uncini broadly hooked. 



Type. Cryptobranchia concentrica, Dall ex Midd. Plate 

 15, fig. 2, a to g. 



Syn. Patella [Cryptohr.) cceca, var. (/9) concentrica, Midd., Sib. 

 Reise, p. 183, pi. xvi, fig. 6. Sept., 1851. 



Patella cceca, Idem, Bulletin Phys. Math. Acad. St. Pe- 

 tersburg, Vol. vi, No. 20, 1847. Schrenck, R. v. 

 Amurl. Moll. p. 291, 1867. 



Lepeta ececoides? n s., Cpr., Suppl. Rep. Br. Ass. pp. 

 603 and 651, 1863. 



Lepeta ececoides, J. G. Cooper, List. Cala. Moll. p. 24, 

 No. 459. Carpenter, Proc. Ac. Nat. Sci. Phila. April, 

 1865, p. 60. 



Sp. ch. — Shell patelliform, of a light brownish or greenish hue, 

 even when weathered. Apex anteriorly directed, — conspicuously 

 so in young individuals ; situated in the anterior fourth. Ante- 

 rior and posterior planes of the shell somewhat arcuate. Surface 

 smooth, with delicate uniform elevated strise radiating from the 

 apex, like threads upon the surface of the shell ; slightly, if at 

 all, interrupted by the concentric lines of growth, which last, in 

 some individuals, are strongly impressed at intervals, but other- 

 wise hardly evident. The number of these impressed lines 

 seldom exceeds three or four. Epidermis extremely thin, brown- 

 ish, generally lost except in very young specimens. Interior 

 smooth, polished, white, often with a greenish tinge. Palleal 

 line complete. Muscular impression narrow, only interrupted 



