22 THE VOYAGE OF H.M.S. CHALLENGER. 
sented only by a small miliary spinelet, or may be entirely absent altogether. I have 
only found them well-developed in one case, and that not the largest specimen in the 
series. In one example I notice a tendency towards diminution in the number of spine- 
lets in the furrow series on the adambulacral plates, and this is shown in the abortion or 
total absence of the outer spinelets at either extremity of the series; as a result of this 
reduction there may be only three, four, or five spinelets in place of six, which appears to 
be the normal number, and the central spinelets of the series appear comparatively long. 
The occasional presence of an additional spine on the actinal surface of the adambulacral 
plates has already been remarked upon. 
Young Phase.—The smallest example in the collection (from Station 46) has a minor 
radial measurement of 3°5 mm., and the rays appear to be comparatively robust. This 
specimen presents in a most unequivocal manner all the characters of the type, and even 
though so young there need not be the slightest hesitation about referring the form to this 
species. So small indeed are the differences between the juvenile and the adult stages, 
that the mature form in this species may well be said to exhibit on a larger scale all the 
features of the embryonic phase. 
In this juvenile example there are no actinal intermediate (ventral) plates. The 
disk and the base of the rays have a somewhat villous or subpapillose appearance, the 
spinelets on the abactinal plates being decidedly robust for the size of the animal, and 
rather thickly covered with membrane. The papulee are well-developed and distinct ; 
and there are three large spiracle-formed pedicellarian apparatus on the disk. The odd 
interradial plates and spines are very large, the latter being about 5 mm. long; and are 
strongly denticulate along the shaft, suggesting to a certain degree the miniature of a 
Cidaris-spine. The knob-like terminations of the tube-feet are large and button-shaped. 
The genital foramina are discernible on each side of the odd interradial plate, opposite 
the first supero-marginal plates and near their inner edge. 
Localities.—Station 50. South of Halifax, Nova Scotia. May 21, 1873. Lat. 42° 
8’ 0” N., long. 63° 39’ 0” W. Depth 1250 fathoms. Blue mud. Bottom temperature 
38°'0 Fahr. ; surface temperature 45°°0 Fahr. 
Station 46. Off the coast of North America, east of New Jersey. May 6, 1873. ° 
Lat. 40° 17’ 0” N., long. 66° 48’ 0” W. Depth 1350 fathoms. Blue mud. Bottom tem- 
perature 37°°2 Fahr. ; surface temperature 40°°0 Fahr. 
Station off the coast of Portugal. January 1873. (Exact date and station not recorded.) 
Remarks.—Pararchaster armatus is characterised by the presence of comb-formed 
pedicellariz on the abactinal area and in the actinal interradial areas, and by their absence 
between the infero-marginal plates. The simplicity of the armature of the infero-marginal 
plates (one lateral spine and sometimes a small companion), and the comparatively large 
number of six or seven spines in the furrow series on the adambulacral plates, also serve to 
readily distinguish this interesting form. 
