162 



PANAMIC DEEP SEA ECHINI. 



becoming smaller towards the posterior edge. The rest of the actinal 

 membrane is covered with irregular rows of small elongate plates radiating 

 from the actinostome. 



The anal system is circular or slightly pyriform (Pis. 75, fig. / ; 78, fig. ' t ) ; 

 it is covered liv live to six irregular rows of concentric and radiating small 

 polygonal plates, a few of which are somewhat larger on the outer margin 

 of the actinostome ; all the plates except those radiating from the actino- 

 stome carry small miliaries. 



A re-exam ina lion of two stages of C. Wyvillii, Figs. 233, 234, collected 

 by the " Challenger," one of IN mm. in length (PI. 80, figs. 5, 4), the 



Fit 



Inside. IS mm. 



233. Cyste< hints Wyvillii. 



Inside. 5G mm. 



Fig. 234. Cystechutus Wyvillii. 



other 56 mm. (PI. SO, figs. 5, 6), shows no great differences between it and 

 C. Lovcni in the arrangement of the apical plates. The increase in the size 

 of the genital pores is marked in the larger specimen (PI. 80, figs. 5, 6) ; 

 they are barely visible in the smaller specimen (PI. 80, figs. .?, 4). With 

 increasing size the slightly elliptical actinal system of 0. Wyvillii (PI. 80, 

 fig. l) becomes pentagonal (PI. 80, fig. 2). The phyllodes are found on 

 a larger number of anibulacral plates (PI. 80, figs. 1, 2). The primary 

 tuberculation is limited to two or three tubercles on each coronal plate, and 

 the miliaries are more distant (PI. 80, figs. J, 3). In the larger specimen 

 the primary tubercles as well as the miliaries have increased in number, 

 so that, compared to the younger stage, they now cover the coronal plates 

 quite uniformly (PI. 80, tigs. .',, 7). In these two specimens of C. WyvUM the 

 anal system is already longitudinally elliptical (PI. 80, figs. /, 7). In the 

 smallest it is covered with three to four concentric rows of polygonal plates 



