1888-89.] Mr John Rattray on the Genus Coscinodiscus. 449 
A Revision of the Genus Coscinodiscus and some Allied 
Genera. By John Rattray, M.A., B.Sc., F.R.S.E. (With 
Three Plates.) 
(Read June 17, 1889.) 
The present paper is a continuation of my monographs already 
published by the Royal Microscopical Society, London, in their 
Journals for June and December 1888. It has been carried out 
under similar conditions in the Botanical Department of the British 
Museum (Natural History), South Kensington, but I am especially 
indebted to Edmund Grove, Esq., E.R.M.S., for much valuable co- 
operation, and to Julien Deby, Esq., for the readiness with which he 
has placed at my command the resources alike of his library and 
cabinet. Herr E. Weissflog and Dr James Rae, R.N., have also 
furnished me with many excellent preparations. 
COSCINODISCUS, Ehrb. emend., Ehrb. Abh. Ber. Ak., 
1838, p. 128. 
Valve circular, rarely regularly or bluntly and irregularly angular. 
Surface flat, often somewhat depressed at centre, and convex towards 
border, or with alternate subcentral elevations and depressions, more 
rarely with a sharply-defined elevated zone, or with one or more 
concentric low undulations. Colour transparent or smoky grey, 
sometimes with concentric zones of different brilliant hues. Central 
space angular or round, hyaline, or with a few isolated granules ; 
rarely apiculate, sometimes indistinct, or replaced by a conspicuous 
or less evident rosette. Markings round and granular or angular, 
sometimes punctiform ; the central papillae prominent, obscure, or 
absent ; rows radial or subradial, often in straight or curved fasciculi, 
those in each fasciculus parallel to that at its centre or side ; 
secondary rows often oblique, curved or straight and decussating, 
more rarely regularly or irregularly concentric ; the opposite valves 
of a frustule sometimes dissimilar; interspaces of varying size, 
usually largest towards centre or opposite the shorter rows, often 
absent. Apiculi few or many, scattered at irregular intervals over 
the surface, or forming one or more circlets near the border ; some- 
VOL. xvi. 25/10/89 2 F 
