1888 - 89 .] Mr John Rattray on the Genus Coscinodiscus. 645 
Exped ., 1886, p. 136, pi. v. fig. 5. — Diam. -18 mm. Central areolate 
area absent. Markings : rays regularly arcuate, rarely substraight, 
2 or 3 short lines diverging from the centre and branching somewhat 
irregularly 2 to 4 times before reaching half the distance to the inner 
ends of the compartments ; the compartments reaching about § of 
radius inwards, their inner ends transversely truncate or slightly 
concave towards the centre, the areolae forming a distinct hand along 
their outer edge and 6, elsewhere in straight oblique decussating 
rows and about 8, in *01 mm., decreasing hut slightly towards the 
border ; the intervals attenuating regularly outwards and reaching 
the border. Border distinct, hyaline. 
Habitat. — Equatorial Atlantic, H.M.S. Challenger (Castracane). 
A. brightwelliana. Grev., Trans. Micr. Soc. Lond ., 1862, p. 48, 
pi. viii. figs. 26, 27. — Diam. *075 to *095 mm. Surface markedly 
convex. Central areolate area absent. Markings : rays straight 
or suhuniformly curved, springing from a somewhat excentric point, 
the compartments reaching about J of radius inwards, their inner 
ends concave towards the centre, unequal, areolate ; a single hand of 
areolae adjacent to their inner ends large, 3 to 3J in *01 mm., the 
others much smaller 6, decreasing gradually outwards to 8 or 9 in 
*01 mm., the intervals of equal breadth (about *0035 to *004 mm.), 
their outer ends reaching the border. 
Habitat. — Springfield deposit, Barbados (Hardman !) ; “ Bar- 
bados” deposit (Greville !); Cambridge deposit, Barbados (Dehy !). 
A crenata. Grev., Trans. Micr. Soc. Lond., 1862, p. 47, pi. viii. 
figs. 4-16. — Diam. *05 to *075 mm. Central areolate area absent. 
Markings : rays straight ; the compartments reaching about J of 
radius inwards, their inner ends concave towards the centre and 
concentric with the border, areolate, a single band of large unequal 
areolae at their inner ends 4 in *01 mm., and from 3 to 3 J times as 
long as broad, beyond this hand 6, decreasing rapidly outwards to 
10 in *01 mm.; the intervals expanding slightly outwards and of 
uniform breadth, reaching the border. 
This species is distinguished from A. concinna by the shape of 
the inner ends of the compartments and from A. vulgaris by their 
regularity. 
Habitat. — Barbados deposit (Greville! Hardman!). 
