58 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



CHAETOCEROS (BACTERIASTRUM) VARIANS (Lauder) Van Heurck 



(Van Heurck, Synopsis, pi. 80, figs. 3-5; H. L. Smith, Types ,No. 57.) 

 The specific name is well chosen, B.furcatum Shadbolt, B. curvatum 

 Shadbolt, and other so-called species belonging here. Nevertheless 

 the aptness of the name has unquestionably led diatomists to refer 

 forms here which a closer inspection would prove to be distinct. The 

 temptation to put any delicate, circular form with radiating setae in 

 this species is like that which has made BiddulpMa polymorpTia the 

 receptable for a good many unrelated species. 

 See under O. medusa above. 



CHRYSANTHEMODISCUS, new genus 



Front (valve) view circular; inverted saucer-shaped, that is, barely 

 convex to within about one-tenth of the radial distance to the mar- 

 gin, then rapidly curving to the margin; a circular and sharply 

 marked central area or umbilicus, about one-eighth of the diameter 

 of the valve in width, covered with round or oval beads, the outer 

 row closely set and forming a perfect circle, those within evenly but 

 not radially arranged; the rest of the valve marked with crowded 

 radial lines or costae, slightly wider at their inner (umbilical) end and 

 barely tapering to the margin, obscurely cross-marked but not divided 

 into beads, somewhat tortuous, with shorter secondary lines so inter- 

 spaced between them that the whole valve is evenly covered with a 

 fine radial marking, as in certain members of the genera Coscinodis- 

 cus, Actinocyclus, etc.; the two valves similar; rim narrow, hyaline. 



This genus somewhat resembles Coscinodiscus and still more nearly 

 Hyalodiscus, from which, however, the strong radial lines and the 

 robust central area covered with large well-formed beads unmistak- 

 ably separate it. The width and ornamentation of the girdle is 

 unknown, as no complete frustules were found. It is also question- 

 able whether or not the frustules grow attached in pairs or chains, as 

 in Hyalodiscus and Melosira; but the finished character of the central 

 area implies that such is not the case. 



CHRYSANTHEMODISCUS FLORIATUS, new species 



Plate 13, 6g. 1 



General characters as in the genus. Mounted specimens frequently 

 split inward from the margin into numerous petallike divisions, be- 

 cause of the convexity of the valve close to the edge and the delicate 

 thinness of the valve between the closely set radial lines or costae. 



Diameter of valve, 0.152 to 0.203; diameter of umbilicus, 0.025 to 

 0.028 mm. Not uncommon in two of the Philippine Islands dredg- 

 ings, one being from the Sulu Island group. 



Type.— Cut. No. 4360G, U.S.N.M. 



