BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 13. AFD. IV. N:0 5. 93 



thickened. This terminal crust is seen already in very young 

 specimens having none but these ventral flattened spines. A 

 close and careful study may decide whetlier it has anv claim 

 to some conncxiou with the epistroma of tlie test; the Echi- 

 nocidaris nigra bears it on the obliqiiely truncated tops of the 

 ventral spines. In the Coelopleuri, however, all the spines, 

 flat and striated on the white imder-side, carinated and sraooth 

 on the coloured upper side, are sheathed with it all över 

 from near the collar. Its consistence al so seems to be diflierent 

 from that of the epistroma. 



Alexander Agassiz remarks of his Podocidaris sculpta^), 

 that it has the general facies of a young Arbacia, and this 

 resemblance is by no means lessened by the aspect of its epi- 

 stroma. The juvenile structure which in the Arbacise gives 

 way, at an early stage, to the subsequent, antagonistic and 

 ultimately prevailing formation of the spinigerous tubercles, 

 is found highly developed in Podocidaris and persistent at a 

 much more advanced age, if not, as it will really appear, in 

 the adult. In a specimen which I owe to the kind liberality 

 of its discoverer, holding 10 mm. in diameter, — one of 17 

 mm. is said to be a very large one, — the entire dorsal side 

 above the equator, more than the half of the whole test, is 

 held by the epistroma and the pedicellariae alone, to the ex- 

 clusion of the tubercles which are conlined to the restricted 

 basal surface, their powerful growth beiug abruptly disconti- 

 nued, all around, close below the ambitus. In the calyx the 

 broad but short costals present each three protuberances in a 

 mesial row, from which exteud ridges, a few directed diago- 

 nally towards the protuberances of the lengthened projecting 

 radials. On the narrow ambulacra, in breadth 0,30 of the in- 

 terradia, each of the two lateral epistromal ridges bears a 

 dense series of up to fourteen high and slender protuberances, 

 while the connectinar ridaes mve rise to nodules and a few 

 lower protuberances. The appearance of the interradia is vfery 

 remarkable. Each of their halves, a and b, has five vertical 

 series of protuberances, the first consisting of two only, near 

 the ambitus; the second of four, from the ambitus upwards; 

 the third and fourth each of seven to eight, reaching from 

 the ambitus to the top; the fifth, sub-sutural, alteruating, of 

 two or three protuberances. The first, second and third series 



') Revision, p. 152, 269, 405, Pl. IV, — Blake Echinoidea, p. 22. 



