60 PALEOPNEUSTES HYSTRIX. 
XXI. Fig. 12). In the apical system of the large specimen figured here 
(PI. XXI. Fig. 3), the maclreporic 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 botli the actinal opening and the anal system do not differ greatly 
in number in the older and very young specimens (compare PI. XXI. Fig.'^. 
13, 14, and Fig.s. 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 fades 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., PI. XIX. Pig. 2 (loTver figure). 
Seen in profile (PI. XIX. Fig. 2) this species is flatter and has a more 
conical outline than P. cristatus. 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, thougli in Lovenia they are longer, and in 
Linopneustes they are as long but not as stout. They resemble more in aj)- 
pearance the spines of a large specimen of PcJiimis aciitus 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 tuberculation of the interambidacral part of the test (PI. XVIII. 
Fig. 2). The ambulacra carry no primary tubercles, only distant milia- 
ries and a few small secondary tubercles in the median interpetaloid space. 
Below the petals the ambulacral plates carry one large primary tubercle 
