REPORT ON THE ECHINOIDEA. 185 



posterior extremity of the test iu a shallow groove ; the test is covered with tubercles 

 of uniform size equally distributed over the plates (PI. XX. figs. 5, 8), except in the 

 lateral posterior interambulacra, where the plates are comparatively bare (PI. XX. fig. 7), 

 as well as on the actiual surface (PL XX. fig. 6), where the tubercles are somewhat larger 

 iu the interambulacral areas and on the actiual plastron. The peripetalous fascicle is 

 broad, pentagonal, with rounded corners; the anterior lateral ambulacra are longer than tlie 

 posterior pair, the latter being comparatively short. The petals are all sHghtly sunken, 

 the odd ambulacral petal is the longest, and its pores are double but not conjugate 

 (PI. XX. fig. 9). 



In the apical system there are four large genital plates ; the right anterior carries the 

 madreporic body (PI. XX. fig. 11); the bivium is separated from the trivium by two large 

 intercalated interambulacral plates. The actinostome is placed in a slight depression 

 formed by the sloping in of the last actinal plates of the trivium and adjoining lateral 

 posterior interambulacra. The posterior interambulacral labium is prominent (PI. XX. 

 fig. 6) ; the actinostome is narrow, transverse, the buccal shields extending from the 

 anterior edge occupy the greater part of the opening. The lateral petaloid ambulacra 

 have broad, flat, triangular feet, with rounded tips (PI. XX. fig. 22), while the suckers of 

 the odd ambulacrum and the other ambulacra outside of the petals have simple feet with in- 

 distinct suckers. The spines are long, cylindrical at the base, and slightly club-shaped at the 

 extremity (PL XX. fig 12) ; from the ambitus to the actinostome they are larger, longer, 

 and pointed, the spines of the actinal plastron are sj^ecially prominent diverging from 

 the median line ; they are spathiform and quite stout. The miliaries are short club- 

 shaped spines (PL XX. figs. 12, 14, 15) simibar to those of the fascioles, only stouter, 

 showing as plainly as possible that the spines of the fascioles are only minute miliary 

 spines arranged in definite rows. I cannot understand why writers on Echinoderms 

 insist continually in bringing up the relationship of the fascioles and of the viliratile 

 chords of the Pluteus and Brachiolarians. To any one who has studied the embryology 

 of Echinoderms, and has followed the homology of the spines, this appears utterly 

 unmeaning. AVhat possible relation there can be l)etween a chord of vibratile cilia 

 such as we find fringing certain plastrons of the Pluteus and the specialisation of 

 calcareous spines remaining in a more or less embryonic stage, and arranged along certain 

 lines which only appear after the young Sea-urchin has reached a considerable degree of 

 development, I am unable to perceive. The intermiliary granulation (PI. XX. fig. 13) 

 reminds us of the intermiliary granulation of such genera as Arbacia, in which these 

 granules are isolated and pass by degrees into club-shaped spines recalling the miliary 

 spines of this species. 



The suckers of the petaloid ambulacra are interesting for their close afiinity to the 

 suckers of the petaloid area of Echinaracliniiis, which form, as it were, the natural link 

 between the fringed suckers of the jietaloid ambulacra of the higher Spatangoids through 



(ZOOL. CHALL EXP. PART IX. 1881) I 24 



