538 Proceedings of Royal Society of Edinburgh. [sess. 
H.M.S. Challenger (Castracane); Jeremie deposit, Hayti (Truan and 
Witt). 
C. ellijpticus. Grun., Reise. d. Novara Wien., 1870 (Bot. Th.), 
p. 104, pi. i. a. fig. 18 a , b. — Elliptical, major axis ‘04 to *075 mm., 
minor *02 to *035 mm. Central space absent. Markings rounded, 
granular ; on the central portion large, subradial or irregular, decreas- 
ing slightly outwards, on a well-defined band at the border minute, 
in radiating delicate crowded striae. 
Distinguished from Cestodiscus ovalis , Grev., by the absence of 
apiculi, and from C. oblongus , Grev. (Trans. Micr. Soc. Lond ., 1866, 
p. 4, pi. i. figs. 9, 10), in the relatively larger size of the central area, 
and the greater diminution of the markings on the marginal band. 
In the explanation of Cleve and Moller’s Diat ., No. 57, C. 
ellipticus is given as equivalent to C. lewisianus , var.; with this 
opinion I am unable to agree. 
Habitat. — Polycistinous Rock, Nancoori (Grunow, Cleve !). 
G. obovatus. Cstr., Diat. Chall. Exjped ., p. 160, pi. viii. fig. 4; 
pi. xviii. fig. 7 ; pi. xxii. fig. 9. — Roundly elliptical or oval, major 
axis '099 mm., about 1 \ times minor. Surface almost flat. Central 
space and rosette absent. Markings polygonal ; towards the centre 4, 
near the border decreasing to 6 or 8 in '01 mm. ; rows straight and 
parallel to the major axis on the central portion, which is distinctly 
defined, and extends to about f of the radius from the centre, 
beyond this in radial rows. 
Habitat. — Pacific Ocean (Castracane !). 
Var. circularis , nov. — Circular. Diam. '0625 mm. Markings 
similar, but the central area less distinctly defined, the rows radiating 
from its outer edge to the border sometimes slightly curved. 
Specimens of this var. have been labelled C. subtilis by O’Meara. 
Habitat. — Humber (O’Meara !) ; stomach of oysters, at Howth 
(O’Meara!); locality? (O’Meara!); Atlantic Ocean, lat. 3° S., 
long. 15° W. (O’Meara!); off Ascension Island, lat. 0° 1'6' S., 
long. 15° 56'5' W., 1845 fathoms, S.S. Buccaneer (Grove! 
Rattray J). 
C. dubius, sp. n. Sch., Atl., pL lxi. fig. 14. — Diam. '094 mm. 
Surface flat from centre for about § of radius, thence convex to the 
