90 
THE VOYAGE OF H.M.S. CHALLENGER. 
covering five (or more) narrow, smaller tooth-shaped ones ; the anal plates are smaller 
than the surrounding plates and irregularly disposed, no distinct valves being visible. 
The largest plates between the mouth and anus measure 5 mm. in diameter. The 
perforated plates of the sole (PL YI. fig. 2) are more or less irregularly formed, in one 
specimen being almost smooth, in another provided with distinct not very numerous 
knobs. So far as I can discover, this form must be very nearly related to Psolus 
operculatus, of which species, however, I have not had the opportunity of seeing any types. 
The specimens dredged at Station 311 are much smaller, the largest being 30 mm. 
long and the smallest 20 mm. The slightly elevated anal portion is devoid of valves, and 
often even at the mouth no larger scales are to be distinguished. The body is covered 
by a large number of scales. The granulation of the dorsal scales is very fine. The 
thin almost transparent sole has only few more or less incompletely developed x - or 
plate-like deposits. These specimens must be closely allied to Bell’s Psolus peronii, 
but differ from it by the form of the deposits in the sole. 
Psolus ephippifer, Wyville Thomson, 1876 (PI. XY. figs. 7-11 ; PL YI. fig. 3). 
Body oval or almost cylindrical, not very depressed, about as high as broad. The 
oral aperture closed by five large triangular valves, and a less regular valvular arrange- 
ment covering the anal opening, which in some specimens seems to lie on the top of a 
small elevation. A double row of pedicels surrounding the sole, those in the outer row 
situated on the inner side of the margin. Anteriorly and posteriorly the odd ambulacrum 
is provided with a few pedicels. The irregular scales do not overlap each other very 
much, excepting round the margin, where they are of minute size. In some specimens 
the scales are almost smooth, in others, on the contrary, distinctly granulated. In the 
female, the dorsal surface has a weU-defined saddle-like elevation formed of large tesselated 
plates of somewhat irregular form and with the surface smoothly granulated. Deposits 
in the sole — numerous more or less crowded, reticulate, knobbed, cup-like plates. Length 
about 40 mm. 
Habitat . — Station 151, February 7, 1874; off Heard Islands; lat. 52° 49' 30" S., 
long. 73° 33' 30" E. ; depth, 75 fathoms; volcanic mud; about forty specimens. 
Station 150, February 2, 1874; lat. 52° 4' S., long. 71° 22' E. ; depth, 150 fathoms; 
bottom temperature, 35° '2 ; coarse gravel; two specimens. Eoyal Sound, Kerguelen; 
depth, 20 to 60 fathoms; one specimen. Marion Islands; numerous specimens. 
Station 145a, December 27, 1873 ; lat. 46° 41' S., long. 38° 10' E. ; depth, 310 fathoms; 
volcanic sand ; one individual. 
Sir Wyville Thomson has already published the supposition that this species is nearly 
related to or possibly a variety of Psolus operculatus, and, indeed, they seem to present a 
great resemblance. It is almost impossible to point out any difference of importance 
