102 THE VOYAGE OF H.M.S. CHALLENGER. 
structure, I have considered it desirable to place them apart; the value of the characters, 
in the present state of our knowledge of the Plutonaster group of species, appearing to 
justify their being ranked as a subgenus. 
1. Lethyaster subinermis, Philippi, sp. 
Asterias subinermis, Philippi, Archiv f. Naturgesch. Jahre. iii. Bd. i. 1837, p. 193. 
Astropecten subinermis, Miiller and Troschel, System der Asteriden, 1842, p. 74. 
Archaster subinermis, Perrier, Nouv. Archives Mus. Hist. Nat., 2° Sér. 1878, t. i, pp. 33, 57, 88. 
Localities. —The Mediterranean area. (Algiers, Naples, Nice, Messina, Sicily.) 
2. Tethyaster parelii, Ditben and Koren, sp. 
Astropecten Parelii, Diiben and Koren, K. Svensk. Vet.-Akad. Handl., Ar 1844 (Stockholm, 1846), 
p. 247, tab. vil. figs. 14-16. 
Archaster Parelit, Sars, Oversigt af Norges Echinodermer, Christiania, 1861, p. 35, tab. 3, figs. 1 and 2. 
- Localities —“ Porcupine” Expedition : 
Station 31. Between the north of Ireland and Rockall. Lat. 56° 15’ N., long. 
11° 25’ W. Depth 1360 fathoms. Bottom temperature 2°-9 C. ; surface temperature 
13°°8 C. 
In Sir Wyville Thomson's popularly written Depths of the Sea, the occurrence of this 
species is specially mentioned on at least two other occasions (loc. cit., pp. 122, 181), but 
the exact localities are not given, and I have not seen any other specimens in the collec- 
tions placed in my hands excepting the one under notice. 
Other localities.—Finmark, Lofoten, Coast of Norway, off Shetland. 
Genus Lonchotaster, Sladen. 
Lonchotaster, Sladen in Narr. Chall. Exp., 1885, vol. i. p. 609. 
Disk rather large. Rays moderately elongate and comparatively narrow, tapering to a 
finely pointed extremity. Interbrachial arcs wide and openly rounded. 
Marginal plates small, short, and numerous, more or less confined to the lateral wall 
of the ray. Supero-marginal plates smaller than those of the inferior series. Infero- 
marginal plates short and broad. The plates of both series covered with low granule-like 
papille, often somewhat squamiform, invested more or less with membrane (succulate). 
No prominent spines on either series. Large incipient pedicellarian apparatus on most of 
the infero-marginal plates, and on some of the plates of the superior series. 
Abactinal area with numerous small closely-packed paxille, composed of small, erect, 
skin-covered papillx, and often bearing a pedicellarian apparatus. Abactinal plating 
circular. The paxille present no definite order of arrangement. Papule regularly 
distributed. 
