188 PANAMIC DEEP SEA ECHINI. 



The test of this species is thin and most brittle. It must have been 

 somewhat conical, the apex slightly excentric posteriorly, with an angular 

 outline, Fig. 255. The oral plastron is very prominent, and separated from 

 the posterior interambulacra by wide, bare ambulacral zones; it is crowded 

 by primaries closely packed carrying long, slender spathiform radioles 

 turned up at the extremity. The actinal lip of the labium is wide at the 

 base, triangular, and extends well into the actinostome (PI. 88, fig. 4). 



The apical system is compact (Fig. 276.) The genital plates are all 

 ankylosed to form an irregularly elliptical central plate (PI. 89, figs. 1, 3), 

 against which abut the small polygonal ocular plates as well as the abactinal 

 plates of all the interambujacra. There are four large genital openings near 

 the anterior part of the central plate ; the anterior pair of genitals are twice 

 as close as the posterior ones. The madreporic openings cover the whole of 

 the posterior part of the central plate and extend bej^ond the genitals so 

 as to cover the greater part of its anterior extremity. The ocular plates 

 are small but most prominent (PI. 89, fig. 3), with large ocular pores and 

 well separated by the intervening apical interambulacral plates. With the 

 exception of there being four genital openings, the structure of the apical 

 system is that of Palgeotropus. 



When seen from the interior of the test (PI. 89, fig. 4) the genital open- 

 ings form, as in Homolampas, deep pits in the outside walls of the stone 

 canal ; this projects fully 8 mm. from the level of the central apical plate. 

 The genital clusters resemble those of Homolampas.' 



The smaller plates of the abactinal part of the ambulacra are bare for 

 a distance from the apex (Pis. 89, figs. 1, 2\ 90, figs. 1, .^); with increasing 

 size the plates carry first a single primary tubercle, then a primary with 

 two or three secondaries placed near the centre of the ambulacral plate. 

 Succeeding plates carry two, three, or more primaries with a few second- 

 aries, and at the ambitus from six to eight or nine distant primaries accord- 

 ing to the size of the specimen. The ambital plates are also comparatively 

 thickly covered with secondary tubercles. 



In the odd anterior ambulacrum (PI. 89, fig. ^') the plates are smaller 

 than those of cither of the lateral ambulacra (Pis. 88. fig. ,2; 90, fig. 2), in 

 both of which they take a great lateral development towards the ambitus. 

 The anterior and posterior as well as the odd interambulacral areas are 

 quite regularly tuberculated (PI. 88, fig. 2 ; 89, figs. /, Q] 90, figs, i, 2, 4). 



1 " Challenger " Echinoidea, PI. XXIV, figs. 6, 7, 12. 



1 



