70 LErETA-riLIDIUM. 



May be known by its rounded form, the ends turned upward, much 

 as in Clypidella pustula. The soft parts are unknown. 



There is an error in the numbers of the plate referred to by Dall. 

 The figure between figs. 3b and 5b represents this species. 



L. ALBA Dall. PI. 40, figs. 38, 3i», 40. 



Shell pure white, smooth or with extremely faint stride ; solid ; 

 interior pure white ; apex directed anteriorly, inconspicuous; shell 

 arcuate before and behind. 



Length of adult 24, width Hi, alt. 10 mill. 



This species differs from the last in its smooth shell, greater size, 

 pure whiteness, greater lateral compression, and generally more 

 rounded back, from the less prominent apex. The tentacula in a 

 specimen twice the size of a concetitrica were not half as large. The 

 teeth differ in the shape of the central tooth and the greatly broader 

 cusps of the laterals, and their striation, resembling those of Pilidium 

 fulvum. 



Aleutian I4ands ; Seniavine Strait ; Plover Bay, E. Siberia. 



Cryptohranchia alba Dall, Amer. Journ. Conch. 1869, p. 145, t. 

 15, f. 3a-d; Proc. U. S. Nat. Mus. i, p. 335, 1S78.— Patella alba 

 AuRiviLLius, Vega-expeditionens Vetenskapliga lakttagelser, iv, 

 p. 318, t. 12, f. 10, 11, 1887. 



Subgenus Pilidium Forbes, 1849. 



Pilidium Forbes, Athenaeum, Oct. 6, 1849, p. 1018. — Forbes & 

 Hanley, Hist. Brit. Moll, ii, p. 440, 1849.— Dall, Amer. Journ. 

 Conch. V, p. 146, 1869. — lothia Gray, (not Forbes) Guide Syst. dist. 

 Moll. B. M., p. 172. — Scutellina Chenu, in part, and of Sars, Moll. 

 Reg. Arct. Norv., p. 122, not Scutellina of Gray and authors. — 

 Not Pilidium Mit>d.,-^= Capulacmcea Sars, (see Capulidce.') 



The dentition of P. fulvum is figured on pi. 40, fig. 43. 

 L. fulva Miiller. PI. 40, figs. 41, 42, 43. 



Shell small, apex strongly inclined forward, near to the front 

 margin ; front slope steep, somewhat concave, posterior slope long, 

 convex ; sculptured with delicate, closely granular radiating threads. 

 Color orange or reddish. 



The form is oval ; apex pointed, prominent. The riblets of the 

 surface are delicate, thread-like, separated by intervals wider than 



