‘PORCUPINE’ DEEP-SEA DREDGING-EXPEDITIONS. 
729 
vessel continuous with the channel formed by processes of the ambulacral plates 
towards the oral end of the ambulacral areas of the corona. The apical disk is very 
wide, 23 millims. in diameter. The ovarial plates are halbert-shaped ; the cleft in 
their outer border is 3 millims. in depth and 3 millims. in width at the base, where 
it meets the corresponding cleft between the interambulacral plates. One of the 
ovarial plates is modified, as in Cidaris, to include the madreporic tubercle. The 
ocular plates are very regularly heart-shaped. The pore for the sense-organ is very 
distinct, about one fourth of the width of the plate from its outer edge. The peri- 
proct is pentagonal, the outer row of plates large and somewhat irregular in form, 
the inner plates becoming smaller towards the central anal orifice, round which the 
final two or three rows converge almost in the form of spines. 
The primary radioles are longest round the ambitus, from 100 to 120 millims. in 
length (Plate LXI. figs. 4, 5), cylindrical or pointed, finely striated longitudinally, with 
some of the ridges prominent and rising into irregular lines of strong spines. The- 
radioles on the apical aspect of the test become gradually somewhat shorter and are 
more pointed (Plate LXI. figs. 6, 7) ; on the oral surface they diminish in size towards 
the mouth, and assume the flattened, curved, grooved, toothed, paddle-like shape cha- 
racteristic of the genus (Plate LXI. figs. 8, 9, 10). The spines of the second series form 
single rows converging towards the base of the principal spines over the alveolae ; they 
are flattened and striated, and about 10 millims. in length. The spines of the third 
series are narrower and more pointed, about 8 millims. in length, and diverge from the 
outer edges of the central band of the ambulacra over the pore-areae. Smaller pointed 
spines are articulated to the smaller miliary granules over the surface of the test. The 
pedicellariae are very remarkable. They consist of two long pointed valves, which, when 
closed, resemble very closely the smaller forms of the flattened spines (Plate LIX. fig. 14). 
Their structure, however, is in every way the same as that of the ordinary three-valved 
pedicellariae, except in the number of the valves. All the usual chambers and ridges 
are developed, and the different muscles are very evident through the transparent walls ; 
they are congregated chiefly on the apical disk and along the edges of the pore-areae. 
The basal portions of most of the large spines for about one third of the length of the 
spines are of a rich deep purple, and the remainder of the spines pale pink. Some of 
the large spines are of a uniform purplish brown, and all the smaller spines and the 
pedicellariae are of a rich purple-brown. 
The dental pyramid is lower and a little wider in proportion than in Cidaris ; but it 
is constructed on the same plan, the epiphyses of the tooth-sockets forming ear-like 
appendages, but not uniting into an arch. The teeth are simply channelled, as in 
Cidaris. The auricles start from the interambulacral areae, in the centre e which the 
two adjacent buttresses of two auricles are soldered together through nearly their whole 
height (woodcut, fig. 2), and only send out a small curved expansion which projects 
slightly towards the ambulacral groove. The tube feet are provided with suckers, which 
are supported by small and irregularly formed calcareous rosettes, and very small calca- 
5 f 2 
