OF ARTS AND SCIENCES. 199 



system. The spines are much longer also, nearly four times the 

 diameter of test, varying but little in shape ; they taper gradually and 

 are covered from tip to base with numerous small spines closely 

 packed in regular rings round the shaft. The number of primary 

 plates is smaller both in the ambulacral and interambulacral areas, 

 the three largest tubercles of the interambulacral area occupying 

 in this species the same relative space of the test occupied by five in 

 Salenia varispina. The large ambulacral tubercles of the actinal 

 region so characteristic of the latter species are not found in S. has- 

 (igera, the actinal tubercles are but slightly larger than the other 

 ambulacral tubercles. — Station 195, 1,425 fathoms; Station 170, 

 630 fathoms; Station 335, 1,425 fathoms; off Cebu, 100 fathoms. 



Podoeidaris prionigera, A. Ag. 



This species is readily distinguished from its "West Indian congener 

 by the greater length of the spines ; they are more regularly tapering, 

 flattened, with very prominent serrations of the two edges. — Station 

 218, 1,070 fathoms ; Station 205, 1,050 fathoms. 



Aspidodiadema, A. Ag., nov. gen. 



This genus is intermediate between the Cidaridoe proper and the 

 Diadematidae. It has, like the latter, a thin test with the spines 

 characteristic of that family. It has, like Centrostephanus, buccal 

 plates. But the primary tubercles are few in number, as in the 

 Cidaridas, occupying with the scrobicular area and accompanying 

 secondary spines nearly the wtiole of the interambulacral plate. The 

 most characteristic feature of the genus is the ambulacral system. 

 The plates, of a nearly uniform size, are small, forming, as in Cidari- 

 dae, a narrow ambulacral system. The abactinal system consists of a 

 narrow ring of ocular and genital plates placed side by side surround- 

 ing a large anal system. Two species were collected by the Challenger. 



Aspidodiadema tonsum, A. Ag., nov. sp., in which the anal sys- 

 tem is protected by five large plates, occupying the greater part of 

 the space enclosed by the genital and ocular ring, and in which the 

 actinal ambulacral tubercles form a double row of tubercles much 

 larger than those of the abactinal region of the ambulacral space, 

 which extends nearly to the middle of the test. — Station 170, Ker- 

 madec Islands, 630 fathoms ; off Cebu, 100 fathoms ; Station 122, 

 356 fathoms ; off Macio, 1,700 fathoms. 



The second species is Aspidodiadema microtuberculatum, A. Ag., 

 nov. sp. It can be at once distinguished from its congener by the 



