70 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



Coscinodiscus; but it can no more be separated from that genus because 

 of its contour, whether studied in its valve or in its girdle aspect, 

 than can Surirella reniformis Grunow be separated from Surirella. 

 Rattray is therefore right (Rev. Cose, p. 548) in preferring the above 

 name, rather than StoscMa admirabilis Janisch issued in his manu- 

 script of the Diatoms of the Gazelle Expedition (1888) and accepted 

 by Schmidt in his Atlas, plate 140, figure 17 (1889). Castracane's 

 name was published in 1887. 



COSCINODISCUS REX Wallich 



(Schmidt, Atlas, pi. 114, fig. 7.) 



This diatom is so fragile that its presence in some gatherings prob- 

 ably remains undetected despite its huge size. 



COSCINODISCUS SCITULUS, new species 



Plate 14, fig. 5 



Valve circular, flat to within one-third of the radial length from 

 the margin, then strongly convex for a half of that distance, whence 

 it slopes gently down to the margin; the entire valve covered with 

 radiating rows of beads equal in size; no central hayline area or rosette, 

 but the beading of the secondary rows so falling short in approaching 

 the center as to leave narrow vacant lines and thereby to produce the 

 "sunburst" effect characteristic of the genus Actinocyclus ; near the 

 margin one or two rows of fine spines irregularly placed, and next to 

 the rim a strong row of short, heavy, blunt processes extending across 

 the rim, thereby giving to it the aspect of being divided into scallops. 



Diameter, 0.052 mm. 



There is a slight resemblance between this and O. bullatus Janisch 

 (Gaz. Exp., pi. 6, fig. 12). 



Type.— Cat. No. 43614, U.S.N.M. 



COSCINODISCUS SUBTILIS Ehrenberg 



(Ehrenberg, Mikrogeologie, pi. 18, figs. 35a-b; Schmidt, Atlas, pi. 57, figs. 

 11-13, 28, 29; Van Heurck, Synopsis, pi. 131, fig. 1.) 



A species of very wide distribution and great variability. 



COSCINODISCUS SYMMETRICUS Greville 



(Micro, Journ., 1861, pi. 8, fig. 2.) 



De Toni (Syl. Alg., p. 1229) excludes the figures bearing this name 

 in Schmidt's Atlas, plate 57, figures 25-27, and probably rightly so. 



COSCINODISCUS TUBIFORMIS Tempere and Brun 



(Brun, Diat., Jap., p. 34, pi. 7, fig. 6; Schmidt, Atlas, pi. 164, fig. 1.) 



The finding of a specimen of this diatom in a Philippine Islands 

 dredging increases a doubt I have had for some time of its being any- 

 thing but a small and robust form of some other species, for example 



