54 P. M. DUNCAN ON THE ECHINODERIVIATA OF THE 



The periproct is large and high up. The height of the vertex 

 is about | of the length of the test. On either side of the vertex the 

 test slopes down in a bold curve to the ambitus. The apical system 

 is eccentric and in advance of the vertex, and is slightly depressed 

 (PL III. fig. 15). There are four large genital openings : the two 

 anterior are closer together than the two posterior, which are sepa- 

 rated by the madreporiform body, which extends beyond the pos- 

 terior ; they are large, and each is more or less perfectly surrounded 

 by a circle of miliary tubercles. The ocular pores are large, and 

 form the angles of a pentagon which incloses the generative tract. 

 There is no groove for the odd anterior ambulacrum, which spreads 

 out towards the ambitus, being bounded laterally by a faint ridge on 

 either side, and crossed by the peripetalous fasciole at about -^ of 

 the whole distance from the ambitus to the apical system. There 

 are a few pores crowded near the apex of the ambulacrum, and a 

 few widely apart between it and the fasciole. 



The anterior pair of petals are widely divergent, lanceolate, 

 slightly pointed externally ; and their poriferous zones are sunken 

 and broad, the hinder ones being the broadest. The pores are 

 rudimentary in the upper part of the front zones ; and elsewhere they 

 are largest in the hinder zones. The pores are nearly round, the 

 external row being more or less ovoid ; they are conjugate, and the 

 ridges intervening between the pairs are raised and ornamented 

 with miliaries. There are from 24 to 26 pairs of pores in the 

 posterior poriferous zones of these ambulacra. The interporiferous 

 space is slightly broader than the posterior poriferous zone, is convex, 

 and ornamented with large miliaries. The posterior pair of petals, 

 rather close to each other, are slightly shorter than the anterior ; 

 they are broader, however, and less pointed at the end. The pori- 

 ferous zones of these posterior ambulacra are sunken, and are nearly 

 equal in breadth ; there are the same number of pores as in the 

 anterior ; and the other details are much the same in both. The 

 interporiferous zone is broader than in the anterior pair of ambula- 

 cra, and is convex and rather above the ordinary level of the test. 



The peripetalous fasciole (PI. III. fig. 15) passes round the ex- 

 tremities of the lateral and of the posterior petals, and across the odd 

 anterior ambulacrum ; it passes behind the posterior petals in an 

 irregular course, but on the whole it is elliptical in its outline in 

 the posterior half, and rather angular and wavy in the anterior. It 

 is situated nearer to the apical system than to the ambitus, except 

 anteriorly, where it is nearest to the ambitus. The tuberculation of 

 the abactinal surface below the fasciole is uniform, and the tubercles 

 are smaller near the fasciole and larger towards the ambitus ; every- 

 where they are crowded, and in many places there are vacant spots 

 like crescent fascioles. The small secondary tubercles in this part 

 are perforate and crenulate, and the scrobicule is often imperfect and 

 oblique, whilst there may not be a perfect miliary scrobicular circle. 

 Above the fasciole and in the posterior interambulacral space the 

 tuberculation is small, and like that of the interporiferous zones, 

 there being neither large secondary nor primary tubercles. In the 



