1888 - 89 .] Mr John Rattray on the Genas Coscinodiscus. 643 
A. rotula. Grev., Trans. Micr. Soc. Lond., 1860, p. Ill, pi. iii. 
fig. 5. — Diam. *11 mm. Central areolate area absent. Markings: 
rays diverging from a central point, simple, or rarely dichotomous, 
straight or slightly arcuate ; on the interradial spaces faint, indefinite, 
narrow dark hands extending for some distance inwards from the 
centro-lateral angles of the compartments ; the compartments reach- 
ing about § of radius inwards, their inner edges somewhat obliquely 
truncate on each side of the rays; areolae faint; the intervals of. 
uniform breadth, their outer ends convex close to the border. — 
Cstr., Atti Accad. pontif. d. nuov. Lincei , 1875, p. 393, pi. vi. 
fig. 3a; A. Grevillii Wallich , var. adriatica , Grun. in Yan Heurck, 
Syn. Diat. Pelg., pi. cxxvii. fig. 12. 
This species is distinguished from those forms .of Asteromphalus 
variabilis having a faintly differentiated subobsolete ray by the 
more straight rays and the less obliquely truncate inner ends of 
the compartments. Peragallo (Diat. \Baie d. Villefranche , Paris , 
1888, p. 74) has already pointed out the identity of Grunow’s 
A. Grevillii ) var. adriatica with A. rotula. 
Habitat. — Monterey stone ( Walk er- Arno tt); Adriatic Sea, Balearic 
Islands (Yan Heurck). 
A . dallasiana. Grev., Trans. Micr. Soc. Lond., 1860, p. 115, 
pi. iv. fig. 10. — Diam. ‘075 mm. Central areolate area absent. 
Markings : rays 7, slightly and uniformly arcuate towards the 
same direction ; the compartments reaching to § of radius inwards, 
their inner ends transversely truncate, areolate; the areolae sub- 
equal 10, near border 12, in *01 mm.; the intervals attenuating 
slightly outwards, and again somewhat swollen at the extremities, 
reaching close to the border. — Asteromphalus dallasianus , Ralfs in 
Pritch. Inf., p. 836. 
Although a centro-lateral area is present there is no such 
subobsolete interval as would be found in Asteromphalus. Compare 
also in this respect some forms of Asteromphalus variabilis. 
Habitat. — Nottingham deposit, U.S. (Greville !). 
A. brebissoniana. Grev., Trans. Micr. Soc. Lond.) 1860, 
p. 114, pi. iii. fig. 9. — Diam. *075 mm. Central areolate area 
absent. Markings : rays sharply bigeniculate about f of their 
length from the centre, two or three adjacent rays meeting 
