‘ PORCUPINE ’ DEEP-SEA DEEDGING-EXPEDITIONS. 
747 
Family 2. Clypeasteid^e, Agassiz. 
Genus Echinocyamus, Van Phelsum. 
j Echinocyamus angulatus , Leske. 
Generally distributed, but not found living beyond 150 fathoms. 
Family 3. Spatangid^e, Agassiz. 
Genus Pourtalesia, A. Agassiz. 
The body is flask-shaped, the anterior extremity abruptly truncated ; the test is then 
almost cylindrical for half its length, contracting gradually from the middle to the pos- 
terior extremity, where it is produced into a long rostrum. A narrow flattened plastron 
occupies the ventral surface, while on the dorsal surface a well-marked ridge runs along 
the middle line from the apex to a point a little way in front of the posterior rostrum, 
where it forms an arched projection protecting a deep pit, at the bottom of which the 
anal opening lies. 
The apical system is produced or disjunct. The three ambulacra of the trivium, after 
passing up from the oral ring, the odd one along the centre and the two others along 
the outer sides of the truncated anterior face, meet directly above the mouth at a point 
where are also four large ovarial openings and a central madreporic tubercle. The 
ambulacra of the bivium, starting from beneath the mouth, diverge and pass one along 
either side of the ventral (interambulacral) plastron until they come opposite the anal 
opening, where they form loops, and return along either side of the dorsal ridge, and 
unite at a point about one fourth of the length of the test behind the point of junction 
of the ambulacra of the trivium. 
The mouth is at the bottom of a deep inversion of the truncated anterior end of the 
test ; it is elliptical, the peristome simple, not bilabiate. Teeth are entirely wanting, 
and there is no trace of either phyllodes or bourrelets. The anal opening is quadrate, 
the membrane of the periproct plated with irregular calcareous scales. 
1. Pourtalesia Jeffreysi, n. sp. (Plate LXX. figs. 1-10 and Plate LXXI.) 
One apparently mature example of this very remarkable urchin was dredged in 640 
fathoms, halfway between Fseroe and Shetland, at a bottom temperature of — 1°T C. The 
total length of the test is 45 millims., and its extreme width 18 millims. ; the height of 
the test from the ventral plastron to the dorsal ridge at its highest point is 20 millims. 
The groove at the bottom of which the mouth lies is very deep — a tunnel-like inversion 
of the test in the centre of the lower part of the truncated anterior end. The mouth- 
opening is elliptical, the peristome simple. The buccal membrane is bare towards the 
centre, and covered towards the outer edge with scales, the larger of which are granu- 
lated and give attachment to small spines and pedicellarise. The odd ambulacrum of 
the trivium starts from the upper entl of the mouth, forms, with a double row of some- 
what irregularly shaped plates, the roof of the mouth-inversion (Plate LXXI. figs. 4, 5), 
