60 PALEOPXEUSTES HYSTPJX. 



XXI. Fig. 12). In the apical system of the large specimen figured here 

 (PI. XXI. Fig. 3), the madreporic body covers nearly the whole of the space 

 between the genital plates ; the two left anterior plates, as well as the right 

 posterior plate, are adjacent and perforated. 



In the specimen measuring 45 mm. in length the apical system, as well as 

 the anal system and the actinostome, had already assumed all the charac- 

 teristic features of the larger and older specimens. 



In the smallest specimen the actinostome is quite pentagonal (PI. XXI. 

 Fig. 13), and the posterior actinal lip only slightly indicated. The plates 

 covering both the actinal opening and the anal system do not differ greatly 

 in number in the older and very young specimens (compare PI. XXI. Figs. 

 13, 14, and Figs. 4, 5). The few comparatively large and distant primary 

 tubercles of the interambulacral plates (PI. XXI. Figs. 9, 10) give to the 

 young Paleopneustes a very different facies from its older stages. 



* Paleopneustes hystrix A. Ag. 



Paleopneustes hystrix A. Ag. Bull. M. C. Z., VIII., No. 2, p. 82, 1880. 

 Saba Bank, Guadeloupe. 21-208 fathoms. 



PL XV III., PL XIX. Pig. .' (lower frgure). 



Seen in profile (PI. XIX. Fig. 2) this species is (latter and has a more 

 conical outline than P. cristalus. I know of no Spatangoid which has such 

 large, stout primary spines as those which cover the interambulacral areas 

 of the abactinal side of the test, though in Lovenia they are longer, and in 

 Linopneustes they are as long but not as stout. They resemble more in ap- 

 pearance the spines of a large specimen of Echinus acutus than of a Spatan- 

 goid. They are straight, comparatively stout, some of the primary spines 

 measuring in length nearly a fourth of the test. These large spines are 

 carried on distant tubercles, not more than three in each of the larger inter- 

 ambulacral plates of the abactinal surface near the ambitus, and only two 

 towards the apical system. Four or five small secondary tubercles irregu- 

 larly placed on the plates, with distant minute miliary tubercles, compose 

 the whole tubereulation of the interambulacral part of the test (PI. XVIII. 

 Fig. 2). The ambulacra, carry no primary tubercles, only distant milia- 

 ries and a lew small secondary tubercles iu the median interpetaloid space. 

 Below the petals the ambulacra! plates carry one large primary tubercle 



