220 BULLETIN OF THE 
sculpture, and there seems to be no serious objection, considering the large 
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 Lovén, 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 (Pseudamusium) imbrifer Lovzn. 
Pecten imbrifer Loven, Ind. Moll. Scand., p. 31, 1846. 
Pecten mammillatus M, Sars (ined.) fide G. O. Sars. 
Pecten Hoskynsi, var. pustulosus VERRILL, Trans. Conn. Acad., V. p. 581, pl. xlii. figs. 
22, 22a, Pl. xliv. fig. 11, July, 1882. 
Pecten pustulosus Verrill, 1. c., VI. p. 261, 1884. 
Pecten Hoskynsi Jeffreys (ex parte); G. O. Sars, Moll. Reg. Arct. Norv., p. 20, pl. 2, 
figs. 1 a-c, 1878; Leche et al., not of Forbes, 1843. 
Plate IV. Figs. 4a, 4b. 
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 lamin, 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, 
lon. 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 Lovén, and is destitute, at any stage, 
of the internal lire 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 imbrifer ; especially when the external sculpture is worn. 
