1888-89.] Mr John Rattray on the Genus Coscinodiscus. 661 
H.M.S. Challenger, lat. 5° 54' K, long. 147° 2' W., 2550 fathoms 
(Hardman!);* Indian Ocean (Ralfs); Gazelle Expedition (Janisch); 
S.S. Buccaneer, off Ascension Island (Grove !). 
Aster om. imbricatus. Wallich, Trans. Micr. Soc. Lond., 1860, 
p. 46, pi. ii. fig. 9. — Roundly elliptical to subcircular. Diam. *06 
to *085 mm. Centro-lateral area clavate, widest at its exremity or 
somewhat nearer to the narrow end, frequently extending across 
and beyond the centre of the valve. Markings: rays sharply 
bigeniculate at their middle, the geniculations regular, forming a 
distinct roundly elliptical figure around the centro-lateral area ; the 
compartments reaching about ^ of radius inwards, their inner ends 
conical, with sides convex, those adjacent to the suhohsolete ray 
with ends obliquely truncate ; areolae obscure, subpunctiform ; 
intervals narrow, at first attenuating, then subequal in breadth, 
their outer ends convex outwards, reaching close to border. — Ralfs 
in Pritch. Inf., p. 837 ; Asterolamyra imbricata, Grev., Trans. 
Micr. Soc. Lond., I860, p. 119, pi. iv. fig. 17. 
Wallich distinguishes as var. /3, forms with “ plani sutures,” i.e., 
non-geniculate rays, and as var. y, forms with “ the capitate 
extremity of the basal ray,” i.e., of the centro-lateral area emarginate. 
To his former var. the name rectiradiata may be given ; the latter 
is unimportant. 
Habitat. — Indian Ocean soundings, 2200 fathoms, Captain Pullen 
(Greville !) ; Bay of Bengal (Wallich) ; Natal (Roper). 
Asterom. hiltonianus. Ralfs in Pritch. Inf., p. 837. — Diam. 
•075 to ‘135 mm. Centro-lateral area slightly constricted at its 
outer sometimes attenuating gradually towards its outer end. 
Markings : rays springing from apex and sides of centro-lateral 
area, straight or subuniformly arcuate, sometimes geniculate about 
their middle, and concave towards the subobsolete interval, rarely 
dichotomous opposite central end of centro-lateral area ; the com- 
partments reaching about f of radius inwards, their inner ends 
sharply conical, those adjacent to the subobsolete interval somewhat 
more obtuse, with sides somewhat convex ; areolse obscure, 20 to 
24 in -01 mm., towards border resolved with difficulty ; the 
In the collection of Mr Julien Deby. 
