200 PEOCEEDINGS OF THE AMERICAN ACADEMY 



larger number of plates protecting the anal and actinal systems, and 

 also by the uniform size of the tubercles of the median ambulacral 

 space along its whole length. The primary spines of this species are 

 stouter and comparatively shorter than those of A. tonsum, some of 

 which are nearly three times the length of the test ; the number of 

 primary plates is less in this species than in the preceding one. — 

 Station 298, 2,225 fathoms ; Station 134, 2,025 fathoms. 



Micropyga, A. Ag., nov. gen. 



Allied to Astropyga, it has, like it, a flat test, short spines, but a 

 more compact abactinal system, a small actinostome with deep inden- 

 tations for the passage of the gills, and primary tuberculation extending 

 both in ambulacral and interambulacral areas to the abactinal system. 



Micropyga tubercidata, A. Ag., nov. sp. 



The spines of the abactinal surface are pointed, while on the acti- 

 nal surface, where the primary tubercles form a closely-packed pave- 

 ment both in the ambulacral and interambulacral areas, the primary 

 spines are club-shaped, and the secondary spines alone are pointed. — 

 Off Cebu, 100 fathoms. 



Asthenosoma pellucida, A. Ag., nov. sp. 



This species, judging from alcoholic specimens, was probably of 

 light green or yellowish color; it is readily distinguished from A. hys- 

 trix, its nearest allied species, by the narrow ambulacral zone and the 

 very regular arrangement of the secondary tubercles in a horizontal 

 row occupying the centre of each primary plate. — Off Cebu, 100 

 fathoms ; Station 192, 129 fathoms. 



Asthenosoma Grubei, A. Ag., nov. sp. 



This species is closely allied to Asthenosema varium of Grube, 

 and these two species may perhaps properly form a separate section 

 of the genus, while such species as A. pellucida, A. hystrix, and A. fenes- 

 trata would form a second subgenus. The material collected by the 

 Challenger is scarcely sufficient to determine this. From the large 

 number of specimens of the genus collected by the Blake, I hope to be 

 able to determine, before the final report is published, the range of 

 variation in one or two of the species. The test of this species is 

 quite tough, the primary plates extremely narrow in both areas, well 

 covered by primary tubercles arranged in one row ; these are larger on 

 the actinal surface and separated by few smaller secondary tubercles 



