MUSEUM OF COMPAKATIVE ZOOLOGY. 221 



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. Hoskynsi being very young and imperfect, while he had only two or three 

 specimens of P. imhrifer. 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 Propeamusium 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) reticTilus Dall. 



Plate V. Fies. 8, 10. 



Left valve less convex and smaller, valves diversely sculptured; right valve 

 with solid uniformly elevated concentric laminae 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, fascicle narrow, close to the border of the valve. Alt. 7.0 ; Ion. 

 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 for a moment an unfamiliar aspect. 



Pecten (Pseudamusium) thalassinus Dall. 



Amussium fenestratvm Verrill, Trans. Conn. Acad., V. p. 582, 1882. 

 AmussiuTA 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 



