96 
THE VOYAGE OF H.M.S. CHALLENGER. 
ment in rows visible, excepting in tbe conical caudal portion, which is characterised 
by five double rows of light brownish pedicels, corresponding to the ambulacra. Only 
the ends of the pedicels are retractile, while the rest is hard, very rough, and more or 
less conical in shape. Perisome thick, hard, leathery, and very rough from numerous 
closely disposed, more or less overlapping tables composed of a mostly elongate or 
irregular fusiform, perforated disk and a long conical spire made up of two rods united 
towards the pointed top. The spire is especially long in the pedicels. Length of the 
contracted specimen about 35 mm. Colour in alcohol, brown with light pedicels and 
tentacles. 
Habitat. — Station 167 a, June 27, 1874 ; Queen Charlotte Sound, near Long Island ; 
lat. 41° 4' S., long. 174° 19' E. ; depth, 10 fathoms; mud; a single complete, contracted 
specimen, and caudal portions of numerous other specimens. 
The only complete specimen I have had at my disposal is rather contracted, so that the 
pedicels appear more crowded than they really may be. Only the caudal portion seems 
to be devoid of pedicels on the interambulacra. The pedicels decrease in size towards 
the posterior extremity of the body, and they are uncommonly rough from the long 
spires of the tables. The anal aperture is surrounded by some small cylindrical papillae, 
strengthened by reticulate plates without spires. The tentacles are retracted, their true 
position being difficult to determine. In conformity with the general condition in the 
genus Thyonidium, the tentacles are unequal and arranged in pairs, five pairs being 
several times smaller than the eight remaining tentacles, which are distributed as three 
pairs and two odd tentacles. Thus, these species deviate from the tjrpical forms with 
twenty tentacles by the circumstance that two of the tentacles are unpaired. 
The calcareous ring (PL V. fig. 5, a) is characterised by having its ten pieces composed 
of numerous small parts ; the radial pieces are prolonged posteriorly and measure 25 to 
30 mm. in length. The figure will give an idea of its construction. I only found a 
single madreporic canal and Polian vesicle. In consequence of the contracted state, the 
retractors are short but very thick ; they seem to be attached at about the middle of the 
body. The respiratory organs are well developed. 
The tables present themselves under very variable sizes and shapes, some being small 
and having a somewhat rounded or angular disk, others being elongate or fusiform, with 
a varying number of holes (PI. V. fig. 5, b and c). The largest tables have a length of 
0'50 mm. or more. The outwardly directed spires attain their greatest length, 0T6 mm. 
or more, in the pedicels. The spire is formed by two rods, united towards the elongated 
conical top, and separated at the base by a hole. At the ends of the pedicels the disks 
become more irregular and rod-like (PI. V. fig. 5, d). The terminal plates of the pedicels 
appear to be rather incompletely developed. 
Thyonidium rugosum is certainly nearly allied to Thyonidium ja.'ponicum, von 
MarenzeUer. 
