12 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



almost absent and with rkaphe strongly or obscurely tortuous; trans- 

 verse stauros sharply distinct but very narrow, not at all flaring 

 toward the ends, which are usually distant from the margins one- 

 quarter the width of the valve. Upper valve as the under one, its 

 median line very narrow. 



Length 0.053-0.091; width 0.031-0.047; 9 lines in 0.01 mm. 



Species somewhat resembling this are — 



A. baldjikii (Schmidt's Atlas, pi. 198, figs. 44-48). 

 A. danica Cleve (Schmidt's Atlas, pi. 198, figs. 60-61). 

 Navicula vaszaryi Pantocsek (Hung. Diatom., pt. 3, pi. 16, fig. 239). 

 A. exigua Grunow (Van Heurck, Synopsis, pi. 27, figs. 29-30). 

 Achnanthidium danicum Flogel (Schmidt, Atlas, pi. 198, fig. 50). 

 A.javanica Grunow (Diat. Siam, Oestrup, pi. 1, figs. 15-16). 

 Its nearest published resemblance is found in the unnamed figure 

 in Schmidt's Atlas, plate 198, figure 49. 

 Type.— Cat. No. 43562, U.S.N.M. 



Genus ACTINOCYCLUS Ehrenberg 



ACTINOCYCLUS BIPARTITUS, new species 



Plate 1, fig. 7 



Valve almost flat except near the margin where the convexity is 

 sudden, its surface sharply separated into two areas, an inner 

 sparsely beaded and an outer densely beaded area; the former with 

 about 25 radii of widely spaced beads, with somewhat shorter rows 

 interspaced between them; this inner area, with a diameter of a 

 little over one-half that of the valve, is surrounded by the densely 

 beaded outer area, composed of the extension of the radiating rows 

 of the former plus other interpolated rows; all the rows slightly 

 tortuous; near the margin of the valve the beading becomes com- 

 pacted into even, closely set rows, the beads progressively smaller; 

 about 25 obscure processes near the margin at the ends of the 25 or 

 more primary radii; psuedonodule minute, evident, close to the 

 margin, surrounded by a small circular hyaline area. 



Diameter 0.079 mm. 



This species somewhat resembles A. sparsus (Gregory) Rattray 

 (Micro. Journ., 1857, pi. 1, fig. 47) and Rattray (Re\. Actinocyclus 

 p. 170); also A. punctulatus Castracane (Chall. Exp., pi. 16, fig. 3) 

 and its variety A. nebulosus Peragallo (Diat., France, pi. 113, fig. 11.) 



Type— Cat. No. 43563, U.S.N.M. 



ACTINOCYCLUS CURVATULUS Janisch 



(Janisch, Gaz. Exp., pi. 5, fig. 8; Schmidt, Atlas, pi. 57, fig. 31.) 



ACTINOCYCLUS DECUSSATUS, new species 



Plate 2, figs. 1-2 

 Surface of valve evenly and densely covered with beading radially 

 arranged, but so spaced as to produce the watchcase pattern seen 

 in Hyalodiscus subtilis Bailey, etc., and to display forty to fifty of 



