5 66 Proceedings of Royal Society of Edinburgh. [sess. 
line. Central space and rosette absent. Markings hexagonal, 
largest and most unequal on a small central area, beyond this 
decreasing but slightly outwards, 8 to 9 in ‘01 mm.; rows radial or 
subradial, the secondary oblique straight or slightly curved rows 
more evident. Border narrow; striae delicate, 8 to 10 in - 01 mm. 
—(PI. II. fig. 19.) 
This genus forms the transition to the genus Asteromyhalus. 
Mr Kitton possesses an abnormal specimen of Arachnoidiscus 
ornatus , Ehrb., from Hong Kong, where the areolae are irregularly 
disposed, and the surface is marked at irregular intervals by well- 
defined straight and curved, branching, or anastomosing lines, which 
seem to be homologues of the costate rays of that species, and 
correspond to the irregularly radial lines of Ooscinodiscus theskelos. 
The radial costae of Stidodiscus Grozierii , Kitton [Month. Micr. 
Jour. t vol. x. p. 275, pi. xxxviii. fig. 2), first found by Capt. 
Crozier in the Mauritius, but also occurring in the West Indies, 
have a similar character. 
Habited . — Santa Marta deposits, Cal. (Doeg !). 
C. duriusculus, sp. n. Sch., Atl., pi. lviii. fig. 8 (no name). — 
Diam. about ’0255 mm. Central space and rosette absent. Mark- 
ings round, granular, about 6 to 7 in -01 mm. ; rows distinct, 
substraight, separated by wide hyaline cuneate interspaces. Border 
sharply defined, broad; striae obvious, distant, 4 to 5 in *01 mm. 
The arrangement of the markings and the border distinguish this 
from all other species. 
Habitat . — Patuxent River (Schmidt). 
C. rotula , Grun. Sch., Atl., pi. lvii. figs. 6, 7. — Diam. about 
•0275 to ’03 mm. Central space circular, ~ of diam. broad, some- 
times excentric. Markings around the central space largest, con- 
sisting of free granules tapering outwards, elsewhere punctiform in 
straight or slightly curved widely separated radial rows ; interspaces 
hyaline. Border sharply defined, with distinct granules opposite 
the ends of the radial rows. 
Habitat . — Campeachy Bay (Schmidt, Weissflog!). 
C. stelliger , Grun. Sch., Atl., pi. lviii. fig. 10. — Diam. about 
•035 mm. Central space circular, P to ^ of diam. broad, bearing a 
