REPORT ON THE ECEINOIDEA. 59 



Podocidaris. 

 PodoeMaris, A. Agassiz, 1869, Bull. JIus. Coiiip. Zool., vol. i. 



* Podocidaris prionigera (PL XXXIV. figs. 14, 15). 



Podocidaris prionkiera, A. Aga.?siz, 1879, Proc. Am. Acad., vol. xiv. p. 199. 



Although Podocidaris scidpta, A. Agassiz, was not uncommon in the dredgings 

 of Mr Pourtalfes, and in those of the " Blake," yet the Challenger obtained only two speci- 

 mens of this species. They both differ from the West Indian species, also collected by the 

 Challenger at Station 24, in liaving a more conical test ; the primary spines are not so 

 distinctly limited to the ambitus (PI. XXXIV. fig. 14) as in Podocidaris scidpta, some of 

 the primary tubercles encroaching irregularly upon the test above the ambitus. The test 

 above the primary spines is much more closely packed with small pediceUariae differing 

 from those figured for Podocidaris sctdpta in the Revision of the Echini (pi. iv. fig. 15), in 

 having a shorter stem and a stouter head. The large specimen had also a single large 

 tridactyle, pyramidal pedicellaria, with slender valves leaving large oj)enings between 

 them above the base. The arrangement of the miliaries, as we find it in tJais species of 

 Podocidaris (PL XXXIV. fig. 14), recalls the somewhat more regular arrangement of the 

 secondaries and miUiaries in horizontal rows in some species of Magnosia and of Codio2^sis 

 as does the presence of large primaries near the ambitus or towards the actinostome. 



The most characteristic differences, however, between the two .species are those of the 

 spines and the structure of the abactiual system. The spines are nearly as long as the 

 diameter of the test, flattened, and comparatively quite slender compared to the broadly 

 lanceolate shaped spines of Podocidaris scidpta. The shnft of the spines of Podocidaris 

 prionigera, although slightly contracted beyond the milled ring, and a trifle broader at a 

 short distance from it, immediately below that part of the shaft where the marginal serra- 

 tions commence, yet decreases very gradually in width, tapering more or less rapidly to a 

 point towards the extremity of the shaft. The serrations of the primary spines are promi- 

 nent, alternating on opposite edges of the flattened shaft ; there are not more than twelve 

 on each edge of a spine measuring 10 mm. in length ; the serrations commence only at a 

 distance of from one-quarter to one-third the length of the shaft from the milled ring. 

 The spines in alcohol were of a brilliant transparent semi-silvery lustre, with a yellowish- 

 brown basal portion. The test brownish -yeUow ; it is not ornamented with deep pits in 

 the median interamljulacral area as in Podocidaris scidpta, and the coronal plates carry 

 above the primary tubercles only the miliaries, irregularly arranged, upon which are sup- 

 ported the short-stemmed large-headed pedicellariae. The plates of the genital ring (PL 

 XXXIV. fig. 15) are arranged much as in Podocidaris scvlpta, the ocular plates, however, 

 are very much larger than those of Podocidaris scidpta ; they are elongated vertically, and 



