84 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



HYALODISCUS CERVINUS Brightwell 



(Quart. Journ. Micro. Sci., 1860, p. 95, pi. 5, fig. 9.) 



This delicate diatom, which Ralfs (Pritchard, Inf., p. 831), 

 O'Meara (Irish Diat., p. 262), and Rattray (Rev., Cose, p. 145) have 

 decided to be a Coscinodiscus has been carefully studied with numer- 

 ous specimens from the Philippine Islands. It proves to be, as 

 Brightwell thought, a Hyalodiscus. Its umbilicus is very small, in 

 some cases almost obliterated, but in others it is quite evident. It 

 is probable Brightwell found such specimens when he named it. 



HYALODISCUS HIRTUS, new species 



Plate 18, fig. 4 



Valve circular, moderately and evenly convex; umbilicus large, 

 heavily rugose, separated from the rest of the valve by a heavy irreg- 

 ularly serrate suture; between this and the rim the valve is marked 

 with closely set rows of beading, generally radial, but somewhat mod- 

 ified to form broad and imperfect fascicles, which are marked off by 

 indistinct intervening rays; midway between the umbilical center and 

 the rim is an indefinite ring of short and blunt spines, superimposed 

 upon the beading; rim very stout, finely cross-marked by rows of 

 indistinct beads, the outermost beads larger and forming a marginal 

 ring. 



Diameter, 0.077; diameter of umbilicus, 0.026; width of rim, 0.005; 

 lines of beading, 13.5 in 0.01 mm. midway. 



There is a faint resemblance between this and Stephanopyxis robusta 

 Leuduger-Fortmorel (Diat. Malaisie, p. 46, pi. 4, fig. 6). 



Type.— Cat. No. 43631, U.S.N.M. 



HYALODISCUS LAEVIS Ehrenberg 



(Ehrenberg, Mikrogeologie, pi. 33, sec. 15, fig. 17.) 



The umbilicus of this species is always much larger than that of 

 Bailey's H. subtilis and its marking, coarser; but even so, the two are 

 rather too close. 



HYALODISCUS PROPEPLANUS, new species 



Plate 18, fig. 5 



Valve practically flat, except for a slight co vexity near the rim; 

 umbilicus large, with strong rugose or vermiform marking, separated 

 from the rest of the valve by a narrow irregular suture ; outside of this 

 the valve covered with closely set, perfectly radial rows of minute 

 beads, becoming barely smaller near to the rim; its surface further 

 marked with frequent dashes or lines, very evenly distributed and 

 radial; rim relatively narrow, marked, with a single row of obscure 

 beads. 



