42 
THE VOYAGE OF H.M.S. CHALLENGER. 
is very rough from the numerous calcareous deposits. The plates, or rather tables, which 
are by far more numerous than the “ anchor-plates,” and give to the integument its rough- 
ness, have a diameter of up to 0'24 mm. or more. Besides these fully developed deposits, 
many others are imbedded in the skin representing the different stages of development 
of the former. The irregularly formed “ anchor- plates ” may be best understood from 
the figures ; their length is about 0 '4 mm. The bodies belonging to the two kinds 
of deposits above mentioned often have a yellowish-brown colour resembling that of 
the small rounded or oval bodies, and I have not seldom met with colourless deposits 
which have begun to change in this respect. 
Genus Trochostoma, Danielssen and Koren, 1878 and 1882. 
Trochostoma violaceum, Studer, 1877 (PI. II. fig. 4 ; PI. XL fig. 1). 
Habitat . — Royal Sound (Kerguelen Islands), 20 to 50 fathoms; numerous individuals. 
Betsy Cove (Kerguelen Islands), January 9, 1874; lat, 49° 16' S., long. 70° 12' E.; 
depth, 20 to 25 fathoms; one specimen. Christmas Harbour (Kerguelen Islands); depth, 
120 fathoms; one specimen. Station 169, July 10, 1874; lat. 37° 34' S., long. 179° 22' E.; 
depth, 700 fathoms; bottom temperature, 40'0 ; blue mud; one specimen. 
The body is fusiform, anteriorly truncated, and gradually decreasing in width 
towards the posterior end, which becomes rather narrow and is devoid of any processes 
or teeth. The tentacles, fifteen in number, are very short and provided with a pair of 
minute processes near their obtuse, round end ; they communicate with fifteen long 
cylindrical tentacular vesicles or ampullse. Each of the five longitudinal muscles is 
divided into two bands, and they do not give off any retractors. The calcareous ring 
(PI. II. fig. 4, d) is built up of ten pieces, five radial and five interradial, which are 
intimately joined together so as to form a continuous whole. The interradial pieces, 
which are much smaller, send forwards one process, while the radial ones have two such, 
one of which is perforated for the nerves. Besides, the radial pieces terminate 
^posteriorly in a large bifurcated process (PL XL fig. 1, a), which supports the corre- 
sponding canal issuing from the water-vascular ring to the tentacles. Polian vesicle 
single, about 25 mm. long. The madreporic canal, single and dorsal, terminates in 
a madreporic tubercle. The reproductive organs are composed of two thin fascicles of 
long cylindrical sacs, one on each side of the medio-dorsal mesentery. The long 
common efferent duct opens externally slightly behind the tentacles, viz., between these 
and the madreporic tubercle. The cloaca communicates with two respiratory-trees, the 
right of which is generally longer, its csecal end being often firmly attached to the 
gullet and the calcareous ring. The pseudhsemal vessels are not brought into connec- 
tion with the respiratory-trees. 
