40 



i'ANA.MIC DEEP SEA ECHINI. 



In Acrosalenia the suranal plate is not always single (PI. 22, figs. £, 6, 

 8), and some of the species indicate a transition between the single suranal 

 plate of Salenia to the numerous plates of the anal system of Echinidae 

 proper, in which no prominent suranal plate exists in the adult. It is seen 

 only in very young specimens of some genera, as those of Strongylocentrotus 

 Temnechinus, Echinus, Toxopneustes, Trigonocidaris, and others, and it is 

 in no way to be distinguished in older stages from the ordinary anal plates 

 filling a part of the anal system, while in Salenia and Acrosalenia the suranal 

 plate is an intercalated one, outside of the anal system (PI. 22, figs. 5, ?), and 

 never becomes a part of the anal system of plates, even when as in Acrosa- 

 lenia, the suranal plate is not single, and there are two or three or more 

 suranal plates (PI. 22, figs. 4, 6, 8), Figs. 55, G2 a, 03, which do not hold 



a definite relation to the primary suranal plate, and may be part of the 

 suranal system either in the direction of the right posterior (PI. 22, fig. 4), 

 the right anterior (PI. 22, fig. 8), or the left anterior ambulacra (PL 22, 

 fig. G) ; or the suranal plate may remain single, Fig. 04 (PI. 22, figs. 5, 7), 

 holding to the anal system the same relation it holds in some of the 

 Salenise. 



In Gauthieria 1 the central part of the apical system is occupied by 

 large hexagonal plates surrounding a central suranal plate, the anal opening 

 is excentric and the posterior genital reduced to a mere narrow shank. As 

 Lambert well says, this is a most unusual structure in Echinidae. The only 

 thino- which at all sue^ests such a structure in recent Echini is the anal 

 system of Aspidodiadcma and Dermatodiadema (PI. 28, figs. 3, ',), which is 



1 Lambert, Bull. Soc. dea Sc hist, et nat. de l'Yomie, September, L888. 



