SPATAGOCYSTIS CHALLENGER!. 



143 



The anal system is somewhat heart-shaped (PI. 70, fig. J), situated in 

 a deep re-entering pocket formed by an overhanging hood of the upper 

 part of the test and the sharp extension of the actinal side into a kind 

 of beak. The anal opening extends the whole length of the rounded 

 anterior lip formed by stouter irregular polygonal plates than the numerous 

 small plates which cover the rest of the anal system. These are larger 

 toward the posterior edge of the anal system, gradually diminishing in 

 size toward the anal slit, where they are quite minute. 



The actinal system is elliptical (PI. 71, fig. 1), slightly pointed, Fig. 177 a ; 

 it is covered on the anterior edge with a few large irregular plates; the 

 rest of the membrane is bare. The actinostome is subcentral, placed near 



Internal view. 48 mm. 



Fig. 208. Spatagocystis C'hallengkri. 



4S mm. 



Fig. 209. Spatagocystis Challengeri. 



the labium. The extent of the odd ambulacral fossa is seen in Plate 71, 

 fig. 2, showing the odd ambulacrum in profile from the actinostome to the 

 ambitus, Fig. 181. 



The apical system of the specimen here figured differs from that figured 

 in the "Challenger" Echinoidea (PI. XXVI a . fig. 8) in having four 

 instead of three genital openings. The anterior pair of genital openings 

 encroach upon four adjoining plates, though the madreporic body covers 

 only the genital plate (PI. 71, figs. J, 4) corresponding to the single anterior 

 genital figured in the " Challenger." The right posterior genital opening 

 is also placed on the suture of two plates. The bivium is separated from 

 the trivium by the anterior zone of the posterior lateral ambulacra (PI. 71, 

 figs. 3, 4). 



Two of the intercalated plates at the apex of the posterior lateral ambu- 

 lacra may possibly be oculars, as they have slight indications of perforations 

 (PI. 70, fig. J). 



