30G 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 paxillas. 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 papulae occupy the interspaces. A number of the plates 

 bear small pedicellarise, the jaws of which resemble those of the entrenched pedicellariae, 

 but are smaller ; and they are placed over a simple perforation in the plate, without the 

 slitdike 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" K, long. 20° 14' 0"W. Depth 1525 fathoms. Hard ground. Bottom tempe- 

 rature 37°"0 Fahr. ; surface temperature 63 o- 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 Nymphaster 

 albidus and Nymphaster basilicus. 



This species is readily distinguished from Nymphaster 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 pedicellarise on the marginal plates. 



4. Nymphaster albidus, n. sp. (PI. LI. figs. 1 and 2 ; PI. 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 48 mm. 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- 



