220 BULLETIN OF THE 



sculpture, and there seems to be no serious objection, considering the laT^re 

 number of species, to retaining the name Camptonectes in a sectional sense, as 

 has been done by Stoliczka, provided it be understood that the division is not 

 known to represent any fundamental diagnostic characters. 



The peculiar sculpture, upon which alone Camptonectes is founded, is not, as 

 was supposed by Stoliczka, singular to Mesozoic species, but may be found on 

 living forms, like P. furtivus Lov^n, and many others. It may exist in un- 

 ribbed species or in those with ribs; in the latter case being supplemental to 

 the other ornamentation. 



Pecten (PseudamuFium) imbrifer Loviiw. 



Pecten imbrifer Loven, Ind. Moll. Scand., p. 31, 1846. 



Pecten ninmmiUatus M, Sars (ined.) fide G. 0. Sars. 



Pecten Hoskynsi, var. pustulosus Verrill, Trans. Conn. Acad., V. p. 681, pi. xlii. figs. 



22, 22 a, PI. xliv. fig. 11, July, 1882. 

 Pecten pnstulosux Verrill, 1. c, VI. p. 261, 1884. 

 Pecten Hoskynsi Jeffreys (ex parte) ; G. O. Sars, Moll. Reg. Arct. Norv., p. 20, pi. 2, 



figs. 1 a-c, 1878; Leche et al., not of Forbes, 1843 



Plate IV. Figs. 4 a, 4 b. 



Valves slightly convex; left one least so, slightly concave at its distal margin; 

 valves diversely sculptured, right valve without perceptible prismatic sculpture, 

 surface smoothish, with radiating series of (larger or smaller) hemispherical 

 punctate bubbles arranged on the slightly raised concentric growth-margins; 

 radiating sculpture of similar nature on the auricles ; left valve with concentric 

 sharp equidistant raised lamina>, wider near the margins and showing more 

 or less prismatic texture ; auricles well defined, the anterior very small, the 

 posterior much larger with strong concentric and faint radiating sculpture ; 

 byssal sulcus very small and fasciole very narrow, passing straight along the 

 body margin ; color vitreous white often with a grayish discoloration. Alt. 12.5, 

 Ion. 12.0, max. diam. 3.3 mm. 



Arctic seas and cold waters north of Europe, the Atlantic, and along the 

 northeastern coast of the United States. 



When the valves are worn, as is often the case, the sculpture on the right 

 valve is represented by more than hemispherical loop-like lines connected by 

 sections of the concentric lines very much as in P. Hoskynsi, which is, however, 

 a smaller species. The pustules vary much in size in different specimens, and 

 have a dotted or cellular surface. 



This fine species was first described by Loven, and is destitute, at any stage, 

 of the internal lirae of Propeamusium, and has a more vitreous and translucent 

 texture than that of P. Hoskynsi, with which it has been widely confounded. 



The range of variation of the external sculpture is very much as in P. Hos- 

 kynsi, and it is difficult to separate young and depauperated specimens of the 

 latter from young irahrifer; especially when the external sculpture is worn. 



