REPORT ON THE HOLOTHURIOIDEA. 
03 
The calcareous deposits of the perisoma itself (PL VIT. fig. 1, h), as well as of 
the pedicels (PL YII. fig. 1, c), are of quite the same conformation. Nevertheless, 
a small difference seems to exist ; as a rule, the disks of the tables of the typical form 
are perforated by four holes, though they often have more, while the disks in the 
Challenger specimen have as a rule four larger central and four more peripheral small 
holes. 
Thyone pervicax, n. sp. (PL V. fig. 9 ; PL XII. fig. 3). 
Body elongate, cylindrical, equally rounded at both extremities. Mouth closed by five 
prominences of the perisome, stellate. The two ventral tentacles considerably smaller 
than the rest. Anus without teeth. Body covered by small, conical, hard, close-lying 
papillse, carrying the pedicels. No arrangement in rows visible. The body -wall very 
thick and hard from crowded deposits of three kinds — cups ; knobbed buttons usually 
with four holes ; and larger, rounded, mulberry-like, scale-like bodies. Pedicels 
strengthened by irregular perforated plates or rods and terminal plates ; the dorsal 
pedicels more conical, and with the terminal plates more rudimentary. Colour in alcohol, 
brownish. Length, 60 or 65 mm. 
Habitat. — Station, Bahia ; depth, 7 to 20 fathoms ; a single specimen. 
This species (PL XII. fig. 3) is remarkable in possessing hard conical papillae crowded 
all over the body, on the top of which the pedicels are situated, thus presenting some 
similarity to Studer’s Trachythyone. The dorsal pedicels do not seem to be so well 
developed as the ventral, their sucking-disks being rounded and their terminal plates 
more rudimentary. The thickness of the perisome, the stellate mouth, and the three 
kinds of deposits point to a certain relation to the genus Colochirus. 
The calcareous ring (PL V. fig. 9, a) is composed of ten simple pieces, the radial with 
a deep incision posteriorly as well as anteriorly, giving the aspect of short, posterior pro- 
longations. The three ventral pieces are slightly smaller than the rest. A single Polian 
vesicle and madreporic canal are present. The retractors communicate with the longi- 
tudinal muscular bands at about the first fourth of the body. The reproductive organs 
are well developed, consisting of numerous slender, simple tubes. The respiratory-trees 
are nearly of the same length as the body itself. 
The outermost layer of the perisome contains the cups (PL V. fig. 9, h), which are 
pierced by four holes, and have the spinous rim directed outwards ; their diameter 
measures about 0'048 mm. The very numerous buttons (PL V. fig. 9, c) are oval, 
0T2 mm. long, and usually distinguished by four holes and a smaller number of large 
knobs. The mulberries are scattered among the former, and have a diameter of about 
0‘4 mm. 
There seems to be reason to refer this species to the genera Oucinnaria and 
