1888 - 89 .] Mr John Rattray on the Genus Coscinodiscus. 547 
absent, a distinct central area *04 mm. broad, bounded by a 
narrow ring of closely disposed minute apiculi. Markings angular 
recognised with difficulty ; within the central area 6, at the borde 
8 to 9 in *01 mm.; secondary oblique decussating rows short, obvious; 
no hyaline band at the border. The connecting zone bears 
straight parallel rows of short striae, 10 in '01 mm., the rows 
separated by narrow hyaline lines. — (PI. III. figs. 2 and 3.) 
Habitat. — “Barbados” (Grove !). 
C. punctatus. Ehrb., Mon. Ber. Ak ., 1884, p. 78. — Elliptical or 
subdiamond-sbaped, major axis -0625 to T2 mm., If to If times 
minor. Central space small, circular sometimes bearing a few 
isolated round granules. Markings rounded, granular, 6 to 8 in 
*01 mm.; interspaces hyaline, largest towards the centre, towards 
the border more crowded ; rows radial, straight ; oblique decus- 
sating; rows evident near the border. Border indistinct on inner 
side ; striae delicate, 8 to 10 in *01 mm. — Ehrb., Mikrog ., pi. xviii. 
figs. 40, 41 ; Ralfs in Pritch. Inf., p. 830 ; H. L. Sm., Diat. Spec. 
Typ ., No. 97 ; Cleve and Moll., Diat., No. 57. 
This species is sometimes mistaken for C. lewisianus, but it differs 
in the arrangement of the markings. It differs from Cestodiscus 
ovalis, Grev., by the absence of obtuse submarginal processes. In 
the original definition Ebrenberg gives the markings as 12 to 13 
in *01 mm. 
Kitton has found frustules with very dissimilar valves in the 
Richmond deposit, Virginia. In one case one valve was normal, 
whilst the second showed a large rounded central area, with round 
isolated granules disposed without order, the zone adjacent to the 
border only appearing normal. 
Grove inclines to associate this form with Adinocyclus, as bis 
forms in H. L. Smith’s series show pseudonodules. 
Habitat . — Richmond, Va. (Greville ! Bailey ! * Grove ! Kitton ! 
Cleve and Moller!); Nancoori (Hardman!); Crescent City, Cal. 
(Weissflog !); Paita deposit, Peru (H. L. Smith !). 
Var. rhombica, nov. C. rhombicus, Cstr., Diat. Chall. Exped., 
p. 164, pi. xxii. fig. 11. — Major axis T19 mm., about 2f times 
* In the collection of Dr Greville. 
