306 THE VOYAGE OF H.M.S. CHALLENGER. 
are hexagonal and diminish in size as they approach the margin, and do not assume the 
form of paxille. A longitudinal series of plates rather larger than the rest proceeds along 
the median radial line, and the other plates are arranged in longitudinal series parallel to 
this. The primary embryonic plates are discernible. All the plates are covered with 
uniform, small, semiglobular, miliary granules distinctly spaced and without any order of 
arrangement excepting a definite marginal series. The granules on the centre of the 
larger plates are the faintest trace larger than the rest. All the plates have the appear- 
ance of being definitely spaced in consequence of the position of the marginal granules, 
though the distance of separation is very narrow. When the granules are removed the 
plates may be seen to be in contact with six adjacent plates by small extensions of the 
respective plates, and that single papulee occupy the interspaces. A number of the plates 
bear small pedicellariz, the jaws of which resemble those of the entrenched pedicellariz, 
but are smaller ; and they are placed over a simple perforation in the plate, without the 
slit-like trench for the disposal of the jaws. 
The anal aperture lies external to the dorso-central plate. 
The madreporiform body is rather large, prominent, button-like, and lies external to a 
pair of plates which appear to be the representatives of the basal plate. Its position on 
the disk is about one-third of the distance between the centre and the margin. The stria- 
tions are fine and numerous. A cycle of rather large plates surrounds the dorso-central 
plate and intervenes between this and the under-basals (°). 
Colour in alcohol, a very light brownish white. 
Locality.—Station 3. South-West of the Canary Islands. February 18,1873. Lat. 
25° 45’ 0” N., long. 20° 14’ 0” W. Depth 1525 fathoms. Hard ground. Bottom tempe- 
rature 37°°0 Fahr. ; surface temperature 63°°0 Fahr. 
Remarks.—A comparative review of the characters of Nymphaster protentus in rela- 
tion to those of its allies will be found embodied in the descriptions of NMymphaster 
albidus and Nymphaster basilicus. 
This species is readily distinguished from NV Viale symbolicus and Nymphaster 
bipunctus by the character of the abactinal radial plates, by the junction of the supero- 
marginal plates in the median abactinal line throughout the ray, and by the absence of 
entrenched pedicellarize on the marginal plates. 
4, Nymphaster albidus, n. sp. (Pl. LI. figs. 1 and 2; Pl. LIII. figs. 5 and 6). 
A single example of a Nymphaster was dredged near the Cape Verde Islands, which has 
a minor radius of 13 mm., and the longest remaining portion of the major radius measur- 
ing 48mm. I am in much doubt as to whether it is an immature stage of Nymphaster 
protentus or a distinct species. Owing to our total ignorance of the actual growth phases 
of Nymphaster protentus, the former view would be purely conjectural ; and as the differ- 
