88 THE VOYAGE OF H.M.S. CHALLENGER. 



"Triton" Expedition: 



Station 10. In the Faeroe Channel. August 24, 1882. Lat. 59° 40' K, long. 7° 

 21' W. Depth 516 fathoms. Bottom temperature 46° Fahr. 



Station 11. In the Faeroe Channel. August 28, 1882. Lat. 59° 29' N., long. 7° 

 13' W. Depth 555 fathoms. Bottom temperature 45° - 5 Fahr. 



Remarks. — This species is readily recognised by the well-developed spines on the 

 supero-marginal plates and the central conical spine on the intermediate or ventral plates 

 in the actinal interradial areas. 



la. ({) Plutonaster bifrons, Wyville Thomson, sp., juv. 



There is a single small example from Station 47a, about which I feel some doubt. It 

 is an immature specimen measuring B=12"5 mm., r=5 mm., and there are fourteen 

 supero-marginal plates. Excepting that the rays are broader at the base and less 

 attenuate, and that the disk is larger, this juvenile accords so closely in all particulars of 

 detail with a similar sized specimen of Plutonaster bifrons, that if it does not actually 

 belong to the type-form of that species there need be little hesitation in regarding it as the 

 young of a very nearly related variety. I cannot think that it is a distinct species. As 

 the adult form has not to my knowledge been met with hitherto in the North- American 

 region, further material is obviously necessary before anything definite can be arrived at 

 with respect to this immature specimen. I have remarked on broad-disked specimens 

 (shown both in the young and fully grown state) dredged by the "Triton," but have seen 

 no reason to give a name to the variety. 



2. Plutonaster marginatus, n. sp. (PI. XIV. figs. 1 and 2 ; PI. XV. figs. 1 and 2). 



Bays five. B — 57 mm. ; r = 16 '5 mm. B < 3'5 r. Breadth of a ray between the 

 third and fourth supero-marginal plates, 13 mm. ; midway along the ray, 8 mm. 



Bays moderately elongate, rather broad at the base, and tapering towards the extremity, 

 which is attenuate. Depressed and comparatively flat, rather thin, and angularly rounded 

 laterally. Interbrachial arcs wide and well-rounded. Disk rather large ; abactinal paxillar 

 area slightly below the level of the marginal plates, probably capable of some inflation. 

 Abactinal surface slightly conically convex centrally ; with a sharp and abrupt median 

 carination along the inner part of the ray. Actinal surface subplane. General form 

 rather thin and depressed. 



The abactinal surface of the disk and rays is covered with numerous, rather small, 

 closely crowded, and uniform paxillae. These have a broad tabulum, upon which are 

 borne twelve to twenty (about fifteen most usually) low and only slightly papilliform, 

 rather large, granules, five or six being central and slightly larger than the surrounding 



