REPOET ON THE ECHINOIDEA. 65 



fig. 10). This genus lias, like Centrostephanus, ten large plates on the buccal membrane 

 (PI. VIII. figs. 3, 7, 11, 14, 15) carrying miliary spines. 



The abactinal system is, as in the CidariclEe, large and circular, but the genital and 

 ocular plates are uniform in size, and form a narrow ring as in Glyphocy2'>hus (PI. VIII. 

 figs. 4, 13) round the membrane covering, as in the Diadematidse, the large anal system. 

 In the genital ring of Centrostephanus rodgersi two of the ocular plates, those adjoining 

 the madreporic plate, are excluded from the anal system. There are in the ambulacral 

 system, as in Hemicidaris and Salenia, two vertical rows of large tubercles limited to the 

 ambitus and the actinal system (PI. VIII. fig. 9), and as in other Diadematidse the am- 

 bulacral system is broad compared to that of the Cidaridse proper (PI. VIII. figs. 5, 9). 

 The interambulacral system has, as in Cidaris proper, only two vertical rows of large 

 primary tubercles (PI. VIII. figs. 5, 8). The test is globular, much as in Amblypneustes. 

 The most remarkable feature of this genus is the structure of the ambulacral system ; the 

 plates composing it are, as in the Cidaridee, small, arranged in two vertical rows, the 

 plates are nearly of a size, and each plate is perforated by a pair of large pores placed close 

 together (PI. VIII. fig. 16). The pores are situated on the outside edge of the plates and 

 run in a vertical line (not undulating as in Cidaris) from the apex to the actinal system 

 (PL VIII. fig. 9). The primary tubercles are perforated and crenulated. The teeth are 

 grooved as in the Cidaridse and Diadematidse. 



In Aspidodiadema tonsum the slender long-headed pedicellariae (PL XLII. fig. 5) 

 are remarkable for the small triangular base of the valve (PL XLIV. fig. 15). The 

 globular short-headed abactinal pedicellarise (PL XLII. fig. 4) differ from those of 

 Aspidodiadema microtuhercxdatmn (PL XLIV. fig. 18) ; in the latter the valves extend 

 into a stout, rather blunt point with smooth edges, while in Aspidodiadema tonsum the 

 short valves are scalloped on the edges and terminate in a powerful hook. 



* Aspidodiadema microtuherculatum (PL VIII. figs. 10-16 ; PL XXXVIII. figs. 17, 

 18; PL XLIV. figs. 16-18). 



Aspidodiadema mierotuberculatuin, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 199. 



This is a larger species than Aspidodiadema tonsum (comp. PL VIII. figs. 1 and 10), 

 and is readily distinguished from it by the smaller number of miliary spines covering 

 the test, their irregular size, and by the more numerous, shorter, stouter, dark violet 

 primary spines carried on the interambulacral area. The colour of the test and spines of 

 all the specimens of this species collected by the Challenger was in alcohol of a- very dark 

 violet, the same is also the case with the large specimens of Aspidodiadema dredged 

 by the " Blake" dming the season of 1878-79. 



In the median ambulacral spaces there are no large primary tubercles, only small 

 secondary tubercles, nearly of uniform size, placed on the inner angle of the ambulacral 



(ZOOL. CHALL. EXP. PART IX. 1881.) I 9 



