MARINE DIATOMS OF THE PHILIPPINE ISLANDS 83 



ment seems to be justified. Of course the perfectly circular form of 

 the valves is against an attempt to refer to it as an endocyst of some 

 unknown Ckaetoceros. However, attention should here be called to 

 the similarity between Hereotheca and the endocyst of Ckaetoceros 

 coronatum Grunow (Nordsk. Nord. Exp., pi. 2, figs. 28-31.) 

 Type.— Cat, No. 43628, U.S.N.M. 



Genus HYALODISCUS Ehrenberg 



For the reasons for including this and Podosira Ehrenberg in one 

 genus see my Diatoms of the Albatross Voyages (p. 240) and for 

 giving the preference to this instead of to the older Podosira see dis- 

 cussion in the introductory part of this paper. 



HYALODISCUS ANNULUS, new species 



Plate 18, fig. 3 



Valve slightly convex, the curvature small until near the rim; 

 umbilicus large, heavily rugose, separated from the rest of the valve 

 by a wide, hyaline and glistening, sutural ring; outside of this the valve 

 rather coarsely marked with diagonal, curved crosslines — " watch- 

 milling " pattern — uniform to the border or rim; the latter wide, 

 with a single row of closely set, minute beads on the inner edge, the 

 outer nearly hyaline, with faint crosshatching. 



Diameter, 0.071; diameter of umbilicus, 0.023 mm. 



Several unnamed figures of this occur, a good one in Janisch's 

 Diatoms of the Gazelle Expedition (pi. 20, fig. 4). 



Type.— Cat. No. 43629, U.S.N.M. 



HYALODISCUS ARGUS (Grunow) Mann 



(Journ. Roy. Micro. Soc, 1879, pi. 21, fig. 6.) 



HYALODISCUS ASPERSUS, new species 



Plate 17, figs. 3-5 



Valve circular, the middle portion about one-half the diameter, 

 very convex, progressively less so to the margin, where it is nearly 

 flat; covered with fine, closely set beading in quincunx pattern, pro- 

 ducing thereby a watch-milling effect, spattered with small irregular 

 beads or blotches crowded about the middle part and flung radially 

 outward, thus curiously imitating a spattered ink blot, scanty half- 

 way to margin, there becoming more abundant; umbilical center 

 very small and obscure; a strong narrow rim, finely crosslined and 

 further maiked with a single row of closely set rectangular beads. 



Diameter 0.082; width of rim 0.0024 mm. 



Type.— Cat. No. 43630, U.S.N.M. 



