82 
THE VOYAGE OF H.M.S. CHALLENGER. 
6 mm. The mouth is closed by five processes or valves, which carry some smaller pro- 
tuberances. The anus is slightly turned upwards, and situated much nearer the dorsal 
than the ventral surface ; it is surrounded by fi ve small conical teeth, alternating with 
five broader scales. 
The perisome is hard and leathery from several kinds of deposits. The rounded or 
oval, thick, reticulate bodies, or, as I prefer to call them, scales, do not attain so large 
a size as in the preceding species, but are, on the contrary, rather small in comparison 
with the size of the animal. Semper seems to deny their presence. The spheres are 
often incomplete and of varying shape (PI. VI. fig. 7a). In the external layer of the 
integument the “hemispheres” or cups are to be found (PL VI. fig. 76); they very 
seldom present a regular appearance, hardly two being alike. In most cases they 
are very slightly concave, perforated by several holes, of which the four central are 
usually largest, and their rim is provided with spines, which are sometimes confined to 
one end of the flat oval plate-like cups. One or several spinous or smooth beams cross 
the cups on their concave side. These cups are much more finely constructed than 
the spheres. The pedicels are supported by terminal plates, numerous transverse 
perforated rods of varying shape (PI. VI. fig. 7c), and perforated, irregular, flat, knobbed 
cups (PI. VI. fig. 7d). 
The three ventral, pieces of the calcareous ring are considerably narrower than the 
rest. A single Polian vesicle is present. Numerous small madreporic canals, of which 
one is slightly larger and situated in the dorsal mesentery, also occur. 
Colochirus cucumis, Semper, 1868 (PL XIV. figs. 9, 10 ; PL VI. fig. 9). 
Habitat . — Station 203, October 31, 1874; lat. 11° 6' N.; long. 123° 9' E. ; 
depth, 20 fathoms ; mud ; a single specimen. 
The body is very distinctly quadrangular, excepting anteriorly and posteriorly, where 
it is pentangular, the odd ambulacrum being there more prominent so as to form a fifth 
angle. The two dorsal angles carry conical tubercles or processes of unequal size, some 
being very small, and arranged in an irregular zigzag row. Moreover, the three ventral 
ambulacra also carry such tubercles anteriorly and posteriorly. The dorsal interambulacra 
have but few tubercles. In the specimen I have seen, the mouth and anus are 
l)ent upwards, and the former is closed by the five characteristic triangular valves. 
No imbricating scales occur round the anus. The three double rows of pedicels 
are very distinct. 
The deposits are of several different kinds — large rounded or oval reticulate thick 
scales ; rounded or oval reticulate spheres, about 0'09 mm. in diameter (PL VI. fig. 9a) ; 
smaller, more delicately constructed spheres (PL VI. fig. 96), about 0‘04 mm. in diameter; 
