26 ALLAN HANCOCK ATLANTIC EXPEDITION REPORT 



the surface is smooth, rounded save for low, faint concentric ridges. The 

 operculum is unique; the lower disk consists of a more or less flattened, 

 circular plaque with 24 to 30 sharply pointed papillae at its periphery (pi. 

 2, fig. 14). The upper cup has 10 major processes, all resembling one an- 

 other; each has a major inwardly directed fang, 2 small spines, one at 

 either side, and a blunt, outwardly projecting boss (pi. 2, fig. 15) ; at the 

 base of each major process, on the inner side of the cup, there is a small, 

 sharply pointed, recurved tooth (pi. 2, fig. 13). 



These specimens differ from H. bispinosa Bush (1910, p. 496), de- 

 scribed from Bermuda, mainly in that the opercular disk in H. bispinosa 

 terminates in about 16 broadly rounded, short crenulations instead of 

 pointed papillae, and the distal cup in 8, instead of 10, major falcate 

 spines. 



M 



