56 PANAMIC DEEP SEA ECHINI. 



Dialithocidaris gemmifera A. Ag. 



DiaUthocidaris gemmifera A. Ag., Bull. M. C. Z. 1898, XXXII. No. 5, p. 75, Plate V. figs, 1, 2. 



Plates 15, figs. 3-0 ; 23. 



A single specimen of this species was dredged in nearly 1800 fathoms 

 about seventy miles southeast of Mariato Point. It is interesting from its 

 size (PL 15, figs. 5-,5), 21 mm., which is nearly twice that attained by species 

 of the genus most closely allied to it (Podocidaris). The abactinal sy.stem 

 is noted for the great size of the ocular plates; these are pentagonal, 

 broader on the genital faces, elongate, tapering to a small face at the 

 ambulacra (PI. 23, fig. 2). The ocular plates are excluded from the anal 

 system (PI. 15, fig. -^)- The genital plates are heptagonal. In the specimen 

 collected there were, as in Coelopleurus, only four bare anal plates, while 

 the' other plates of the apical system are well covered with irregularly 

 arranged sessile verrucae varying in fonn from globular to club shnpe. The 

 madreporic body is well developed, but the genital openings cannot be 

 traced from the exterior in ti)e clusters of verrucas and miliaries. 



The primary interambulacral tubercles extend only to the fourth or fifth 

 plate from the abactinal system, those of the ambulacral rows somewhat 

 higher (Pis. 15, figs. 4, G ; 23, figs. 2, >'). The interambulacral primaries 

 (PI. 2o, fig. 12) are placed at each extremity of the plate, the greater part 

 of the remainder of the plate being covered by irregularly arranged 

 miliaries (PI. 23, figs. 7, 3). \\\ the thiid and fourth plates above the 

 amljitus the interambulacral primaries become smaller (PI. 23, fig. 3)\ 

 sessile verrucoB (PI. 23, fig. 11) are found between them in addition to the 

 miliaries. In the followiuo- plates the inner primary disappears, the 

 verruca? increase iu number, and are arranged in a line parallel to the 

 sutures along the central part of the plates. In the last three and four 

 abactinal plates they extend the whole length of the plate, the lower part 

 of which is bare and slightl}^ sunken ; the upper, above the verrucJB, is 

 covered with miliaries. 



Tile ambulacral plates carry but a single primary tubercle, fully as large 

 as the adjoining primary interambulacral ones, Fig. 86. The primary 

 tubercles graduMlly disappear on tiie abactinal parts of the ambulacrum to 

 be replaced by one or two sessile vcrruciD and large miliaries. 



Tilt' ambulacral pores form n vortical line with the pairs of pores placed 



