A. E. Verrill — Study of the family PectinidcB. 83 



Cyclopecten pustulosus Yerrill. (See page 70, fig. 1.) 



Pecten pustulosus Verrill, Amer. Journal Scieoce, vol. v, p. 14, 1873; Trans. Conn. 

 Acad., vol. iii, p. 50 : vol. v, p. 581, pi. 42, figs. 22, 22a; vi, p. 261; Expl. by the 

 Albatross, p. 577, pi. xxxi, figs. 142, a, &, 1885. 



Pecten {Pseiidamusium) imbrifer (pars) Dall, Bull. Mus. Comp. Zool., xii, p. 220, 

 1886 (not the figures), {non Loven). 



Plate XIX. figs. 3, 4. 



In this species the ligament is thin ; there is a narrow, simple, 

 cardinal ridge, with faint tranverse denticulations and striae. The 

 chondrophore is small, excavated in the thickened margin of the 

 hinge-plate in both valves. There are no auricular crur?e. 



The nucleus projects above the hinge-margin in the upper valve, 

 but not in the lower. The posterior auricle is small in both valves, 

 but has a prominent outer angle. The byssal notch is small and 

 narrow, with its margin incurved or sinuous ; there are no pecti- 

 nidial teeth. The valves close pretty tightly, leaving only a slight 

 subauricular slit. The inside of the valves often has a subnacreous 

 luster. There is no flattened submarginal area in either valve. 



This species has been referred to Propeamiisiwn Hoskynsi by 

 Jeffreys, and to C. imbrifer by Dall. It never has internal ribs, like 

 the former, which it resembles in sculpture. From the latter, as 

 originally described by Loven, and re-described and figured by G. 

 O. Sars, it differs especially in the character of the ornamentation of 

 the left valve. 



The European form has the vesicles much less crowded in each 

 radial row, subconical and mucronate, while in ours they are usually 

 closely crowded and often even in contact in the radial rows ; their 

 form is either rounded or elliptical, with the longest diameter in the 

 direction of the concentric lines, and the summit is evenly rounded, 

 showing no tendency to the subconical or mucronate form. When 

 perfect they resemble small blisters with the surface roughened or 

 minutely granular under the microscope ; when broken or worn off, 

 as frequently happens, the basal part remains in the form of semi- 

 circular or semi-elliptical, imbricated, arched scales, usually consid- 

 erably elevated above the surface and connected by very delicate 

 concentric raised lines. The anterior auricle of the left valve is 

 roughened by the close, elevated, concentric lines and by from four 

 to six well-marked radiating ridges or ribs, upon which the concen- 

 tric lines form regular elevated arched projections, often so crowded 

 as to be imbricated ; in some young examples, like the one figured, 

 the concentric lines on the auricle are less crowded, and only two or 



