160 



PAXAMIC DEEP SEA ECHINI. 



to indicate a partial resorption of a part of the tubercles. This is still 

 further elucidated in specimens of C. Lovcni. When coining up in the trawl 

 most of them appeared as if patches of the test had been badly rubbed ; 

 they had lost their purple color, and the tubercles seemed broken off 

 (Pis. 75, fig, 2 ; 76, figs. 1-3). A closer examination of these white patches 

 (Pis. 77, figs. !-', ; 78, fig. .') showed that they consisted of bare areas 

 where the miliaries as well as many of the primaries had disappeared. In 



other parts of the test the scrobicu- 

 lar areas alone remained to show the 

 position of the small primaries, the 

 mammelon and primary boss having 

 disappeared (PL 77, figs. ;?, 3). This 

 is well seen in the actinal plates of 

 the odd interambulacral area (PI. 77. 

 fig. /) and on the sides of the test 

 near the ambitus (PI. 77, figs. 3, _',). 

 Nothing, it seems to me, can show 

 mure plainly the constant struggle 

 that must exist for the deposition of 

 the needed carbonate of lime even 

 for such thin tests as those of C. 

 Loveni or the shells of the delicate 

 deep-sea mollnsks associated with 

 them, the least disorder in the growing tissue of any part of the test evi- 

 dently affecting at once the active deposition of the carbonate of lime of 

 that region. 



Tn the apical plates of Cystechinus, Fig. 228, the odd anterior ocular 

 is followed by the madreporic genital plates, composed of the anterior 

 genitals followed by the large lateral anterior adjoining oculars and the 

 elongate posterior genitals against which abut the large lateral posterior 

 oculars (PL 79, figs. 1-3). 



In the three larger specimens of which we examined the apical system, 

 Fig. 229, there was considerable variation in the shape of the apical plates. 

 In one case (PI. 79, fig. t) the plates of the abactinal lateral interanibulacra 

 of both the zones abutted against the sides of the anterior madreporic 

 genital, in the others (PL 79, figs. .', J) the plates of the posterior zones 

 terminated against the anterior lateral oculars. These, as well as the pos- 



Luside view. 80 nun '.' 



Fig. 228. Cystechinus Loveni. 



