‘ PORCUPINE ’ DEEP-SEA DREDGING-EXPEDITIONS. 
743 
membrane is mailed with densely imbricated plates, those which continue the ambulacral 
series of the test being perforated by double pores up to the edge of the mouth ; and the 
whole are studded, on their outer exposed edges, with tubercles for short spines and for 
pedicellariae of the two smaller forms. 
The dental pyramid is rather higher in proportion to its width than in C. hystricc, 
and much higher than in Phor mosoma placenta. The epiphyses of the jaws are much 
larger, and form curved ascending processes almost as in Liadema , but they do not unite 
into an arch. The teeth are broad and simply and uniformly grooved ; they come some- 
what rapidly to a point at the extremity. 
The arrangement of the internal organs is remarkable. It is probably the same, or 
nearly the same, in all the members of the family which have been described ; but the 
largest specimen of the present species which we procured was torn open and a good 
deal injured, which gave an opportunity of working out the general arrangement of its 
parts without sacrificing a unique specimen. A strong fibrous fascia (Plate LXVI. 
fig. 3) rises from the inner surface of the ambulacral plates near their outer ends, and 
forms a kind of diaphragm nearly dividing the cavity of the test perpendicularly on each 
side of the ambulacral area, and thus inclosing the ambulacral organs (nerves, vessel, 
and vesicles) and cutting them off from the rest of the body-cavity. This diaphragm 
does not run up as a complete wall to the edge of the peristome and periproct, but a 
kind of notch is left towards the centre of the body-cavity to allow the passage of the 
intestine. At this point the fascia rises up from each side of the ambulacral area as 
elsewhere ; but instead of joining the fascia from the opposite wall of the test, its fibres 
unite with those on the opposite side of the same ambulacral area, and take the form of 
a cribriform membrane, which thus closely arches over the ambulacral organs. The 
intestine, in passing round the body-cavity, is thus restricted, as it passes the ambulacral 
areas, to these notches, while in theinterambulacral spaces it forms wide loops suspended 
from the interior of the test by delicate mesenteric membranes and filaments (Plate 
LXVI. fig. 4). This arrangement of fibrous fasciae reminds one strongly of the arrange- 
ment of the calcareous plates and trabecula; in the Clypeasters. The fascia is continued 
at the apical pole into a broad band which passes round the margin of the periproct, 
including in a common sheath the circular ambulacral vessel and the genital ducts 
(Plate LXVI. fig. 3). The ovaries are very long and narrow (Plate LXVI. fig. 3), and 
occupy the centre of the interambulacral areas to the circumference. 
The ambulacral vessels send off a straight simple branch to each pair of pores, the 
branch dilating as it approaches the pores into a pyriform vesicle (Plate LXVI. fig. 5). 
The tube feet on the ventral surface are cylindrical ; their walls are supported by irre- 
gularly shaped cribriform plates (Plate LXVII. fig. 9), and are provided with a terminal 
sucker with a calcareous rosette. The tube feet on the apical surface are long and 
conical, and taper to a point, without a terminal sucker. 
The colour of the test generally is greyish, but ten wide bands of purplish brown 
radiate from the apical pole, shading off into the grey of the test, and giving a rich effect 
MDCCCLXXIV. 5 H 
