88 
THE VOYAGE OF H.M.S. CHALLENGEE. 
the case in P solus operculatus. The deposits of the sole are very densely crowded, being 
larger, more plate-hke, and provided with more holes than in the forms dredged at 
Station 49. In some specimens a few pedicels may he found on the odd ambulacrum. 
P solus antarcticus, Philippi, 1857 (PI. XV. figs. 3, 4 ; PI. VI. fig. 1). 
Habitat. — Station 308, January 5, 1876 ; lat. 50° 8' 30" S., long. 74°41' W.; depth, 
175 fathoms; blue mud; six specimens. Station 320, February 14, 1876; lat. 
37° 17' S., long. 53° 52' W.; depth, 600 fathoms; bottom temperature, 37°'2; green 
sand ; a single very small specimen. 
Though this species is doubtless nearly allied to the northern forms, especially 
Psolus squamatus, it difiers considerably in several important points, and a 
comparison of the Arctic and Antarctic representatives will clearly show that they are 
distinct. The six specimens I have had at my disposal were all collected near the 
west coast of Patagonia, not far from the Strait of Magellan, so there can be but 
little doubt that they really belong to the species described by Philippi. 
The largest specimen has a length of 50 mm. The body-form is like that of 
Psolus squamatus. The mouth is closed by five very large triangular valves, the sides 
of which are almost equal. In the largest specimen, which I am about to describe, the 
length of the sides of these triangular scales is 9 mm.; their slightly curved bases, being 
distinctly marked, give rise to a circular or angular ring. In two of the specimens, 
however, some of the oral scales are parted in two, thus presenting a more irregular 
arrangement. In the same manner, the anal aperture is closed as a rule by five 
distinct though much smaller scales, which give rise to a smaller anal circle round 
their base. The scales are almost smooth or very finely granulated, and do not overlap 
each other so much as is the case in the Arctic forms, and those which lie close to the oral 
scales seem often to be of considerable size. Very mmute scales surround the margin 
of the dorsal surface. Seven to nine scales occur between the oral and anal scales. In 
aU the specimens I have seen the scales have a brownish colour, excepting round the 
free margin, where a broad brim of a light greyish colour occurs. 
The flat ventral sole is constantly surrounded by only two rows of pedicels, the exterior 
of which is situated . in the sharp margin itself and contains much smaller pedicels. 
Anteriorly, and sometimes posteriorly, the odd ambulacrum carries very few — two, three, 
or four — pedicels. The deposits in the sole (PL VI. fig. 1) consist of irregularly per- 
forated plates, with in most cases numerous distinct knobs ; very seldom a plate devoid 
of knobs is to be found. Sometimes the plates are slightly hollowed so as to take the 
shape of very flat cups. 
I have been able to compare this species with equally large specimens of Psolus 
fahricii and Psolus squamatus. I never found in them the well-marked oral and anal 
