1888-89.] Mr John Rattray on the Genus Coscinodiscus. 635 
A. ralfsiana. Grey., Trans. Micr. Soc. Lond., 1862, p. 50, 
pi. viii. fig. 31. — Diam. *07 to ‘08 mm. Central space sub-circular, 
•0025 to '003 mm. broad, sometimes slightly excentric ; an evident 
subcentral areolate area reaching between \ and i of radius from 
centre. Markings on subcentral area unequal, 2^ to 4 in *01 mm., 
the smaller sometimes confined to a band contiguous to the central 
space ; rays many, straight, those on one side of valve sometimes 
somewhat longer than those on opposite side ; the compartments 
reaching from -j to Afr of radius inwards, outline obtusely conical, 
sides subuniformly convex, non-areolate but with distinct subradial 
lines at intervals of ‘0025 to *003 mm., frequently dichotomising 
towards the border ; intervals wide, reaching close to the border ; 
adjacent to the border a circlet of delicate subregular striae, 4 to 4J 
in. *01 mm. — Eul., Diat. Spec. Typ., No. 16. 
Habitat.-— -Barbados deposit (Greville ! Grove, Eulenstein !); 
Cambridge deposit, Barbados (Deby !). 
§ 3. SUBMARGARITACE/E. 
Aspect subpearly. A central space usually distinct. Rays 
broad or undifferentiated, the inner ends of the compartments 
extending to edge of central space. 
A. ambicfua. Grev., Trans. Alter. Soc. Lond., 1862, p. 54, pi. viii. 
figs. 42-45. — Diam. '0175 to *0525 mm. Central space angular, 
distinct, hyaline, up to about *01 mm. broad. Markings : rays 
straight, sometimes slightly constricted at the middle or expanding 
regularly outwards and merging into the compartments ; inter- 
radial spaces expanding outwards, at outer end trilobate, the 
small central lobe homologous to the interval between the com- 
partments ; two straight or slightly curved lines (concave towards 
each other) passing from the inner end of this lobe, and meeting 
at or near the inner ends of the interradial spaces ; the compart- 
ments reaching about of radius inwards, sometimes indistinctly 
defined, subhyaline ; small isolated round granules sometimes 
present close to the sides of the interradial spaces. 
Rarely the outline of the valve is obtusely angular. 
Habitat. — Cambridge deposit, Barbados (Johnson !) ; Barbados 
(Greville !) ; locality 1 (Deby !). 
