MUSEUM OF COMPARATIVE ZOOLOGY. yan d 
After a careful study of the specimens in the Jeffreys collection, I am not 
surprised that he should have united them, the majority of his examples of 
P. Hoskynst being very young and imperfect, while he had only two or three 
specimens of P. imbrifer. The latter is a cold-water species, reaching its 
finest development in arctic or subarctic seas; it is doubtful if it reaches as far 
south as the coast of France on that side of the Atlantic, unless in very cold 
and deep water. On the other hand, no species of Propeamusiwm has been 
found in the arctic seas. I have not seen P, leptalea Verrill, but the diagnosis 
reads much like a description of one of the more finely sculptured forms of 
imbrifer. 
Pecten (Pseudamusium) reticulus Datt. 
Plate V. Figs. 8, 10. 
Left valve less convex and smaller, valves diversely sculptured; right valve 
with solid uniformly elevated concentric lamine crossing thread-like rather 
distant radiating riblets ; where the lamina crosses a thread, especially near the 
margin, it rises into a minute grooved spine; auricles similarly sculptured ; 
surface showing the prismatic texture in a very delicate manner ; left valve 
also prismatic, with some strong radiating sculpture on the auricles, but the 
body of the valve marked with fine concentric, uniform, wavelike undula- 
tions; auricles well marked, the anterior the smaller; byssal notch rather 
deep, fasciole narrow, close to the border of the valve. Alt. 7.0; lon. 
7.25 mm. 
Obtained in 82-123 fms. at Barbados. At Station 297, where the specimens 
were living, the bottom was stony, and the bottom temperature 56°.5 F. 
This species is among the Pseudamusiums what A. cancellatum is among the 
Propeamusiums. It is differentiated from the following species by the char- 
acters mentioned under the latter, and appears to be always pure white. There 
were six strongly pigmented, proportionally very large, ocelli on the mantle- 
edge of the left valve. In the very young the reticulation in a concentric sense 
is sometimes looped, which at first gives it a different aspect. By accidents 
of growth the radiating sculpture and its spines are sometimes not rectilinear 
from the umbo, which also gives it fora moment an unfamiliar aspect. 
Pecten (Pseudamusium) thalassinus Datt. 
Amussium fenestratum Verrill, Trans. Conn. Acad., V. p. 582, 1882. 
Amussium sp. Verrill, Ibid., VI. p. 261, 1884. 
Left valve less convex and slightly smaller; right valve sculptured much 
as in reticulus, but less pronounced and without spines, sometimes nearly 
smooth except near the margin, where traces of the radiating sculpture are 
always visible ; auricles as in reticulus, but less strongly sculptured ; left valve 
with concentric sculpture coarser than in reticulus, notch similar ; prismatic 
