174 



PANAMIC DEEP SEA ECHINI. 



In Palaeobrissus ^ the ambulacral plates widen very regularly from the 

 apex to the ambitus, as in Argopatagus, without the break forming the ill- 

 defined petaloids of Genicopatagus. The 



HE 



pores, however, form diverging lines and 

 increase regularly in size, much as they do 

 in Paleopneustes. In the apical sj'stem of 

 Palaeobrissus the anterior genitals are united 

 in one plate carrying the madreporic body,, 

 and the posterior genital plates are distinct, 

 though in contact, — a combination which has 

 not been noticed in other Spatangoids. 

 . From the position of the anal system and 

 the structure of the actinostome, Genicopata- 

 gus has somewhat the facies of Paleopneustes, while the outline of Phrisso- 

 cystis and Argopatagus are quite similar. Fig. 255. 



Fig. 254. 



37 mm. 

 Genicopataou.'^ AFFIXI.S. 



Fio. 256. 



1 AkGOPATAOUS VITREUS. Dorsal. 48 mm.? 2 OeNICOPATAGUS AFFIXI8. Domal. 37 mm. 



3 PALKOP.NKUSTKS HYSTUIX. Ventral. 153mm. 4 PURISSOCYSTIS AriLEAT.^. Domal. 120mm. 



1 "Blake" Echini, PI. XXIV. figs. 10-12. 



