REPORT OIST THE HOLOTHXJRIOIDEA. 
75 
jSiO other differences between the present and the two former specimens are to be 
fonndj except the fact that the calcareous deposits are smaller^ and have fewer holes bnt 
they are often more closely knobbed; moreover, the handle is more minute. They 
measure Off 4 or OT 5 mm. in length. Among these deposits one may find smaller almost 
roundish knobbed plates with only a few (four or five) holes and no handle, or only a rudi- 
mentary one, recalling those in Cucumaria Icevigata. In this respect it seems that the 
variety intermedia forms a transition between var. marionensis and the typical cucu- 
maria serrata. One of the specimens dredged at Marion Islands measures about 55 mm. ; 
that part of it which is fully extended has only a simple zigzag row of pedicels on each 
ambulacrum, while the more contracted parts of the body have the pedicels in double 
rows. The Polian vesicles and a single madreporic canal are present. 
Genus Ocnus, Forbes, 1841. 
Ocniis typicus, n. sp. (PI. XIV. fig. 11 ; PL VI. fig. 10). 
Body narrow, elongated, tapered towards each extremity. Pedicels in a simple row 
along each ambulacrum, rigid, not retractile. The interambulacra naked. The ventral 
ambulacra with about twenty, the dorsal with about fifteen pedicels. Deposits of three 
kinds — large, thick, rounded, or oval scales; small, irregular, knobbed buttons; and 
minute dichotomously branched bodies or rosettes. Length of the largest specimen 
about 40 mm. 
Habitat. — Hong Kong, at a depth of 10 fathoms ; two specimens. 
The body of this typical Ocnus is very elongate, slightly more tapered posteriorly 
than anteriorly. In one specimen the body is rounded and fusiform, in the other pent- 
angular. Both specimens are more or less strongly curved. No anal teeth are present. 
The tentacles are retracted. The pedicels are hard, directed straight out from the body, 
and seem not to be capable of retraction. They are distributed in five very distinct 
simple rows, arranged in straight lines only, as is common in several northern species. 
The perisome is very hard, leathery, and the scales do not imbricate, but are visible 
externally as rounded larger or smaller darker spots. The scales are round or ovate, 
thick in the middle, decreasing towards the margin ; they are built up of a strong- 
calcareous network, and the largest have a diameter of 0'8 mm. to 1 mm. The buttons 
(PI. VI. fig. 10a), about 0‘06 mm. in diameter, present themselves under very different 
forms, having very seldom a symmetrical appearance. They are mostly irregularly 
rounded or oval, with a few, four to six, perforations, and with the margin uneven from 
the often rather prominent knobs which are situated on it. One or two knobs are also 
to be found in the middle of the buttons. The rosettes (PI. VI. fig. 105) are very 
