RHOICOSPHENIA. 



275 



var. vulgaris Grun. (Sphenella vulgaris Kuiz. ; H.V.H. Atl., pi. 25, 

 f. 21*; in Type No. 221), plate 7, fig. 316. 



Smaller and more strongly clavate. Length, 2 to 2^25 c.d.m. 



Fresh water. Common. 



G. exiglllim Klltz. (Baa, p. 84, pi. 30, f. 58; H.V.H. Atl., pi. 25, 

 f. 34; in Type No. 356), plate 7, fig. 317. 



Valves narrowly and regularly cuneate, with upper apex obtuse, a little 

 narrowed. Raphe surrounded by a feeble hyaline zone. Striae sub-parallel, 

 quite equally approximate to raphe, about 18 in 1 c.d.m. Length, about 1*5 

 c.d.m. 



Marine. Ostend, mixed with a gathering of Grammatophora oceanica (Westendorp), England 

 (Norman), Calvados (Br^bisson), Cuxhaven, Denmark, Heligoland. 



var. minutissima. (H.V.H. Atl., pi. 25, f. 38*; in Type No. 536), 

 plate 7, fig. 318. 



Much smaller than the type form. 



Same gathering. 



GENUS 28. 



RHOICOSPHENIA GRUN. 

 i860. 



a. h. c. 



Fig. 59. Rhoicosphenia 

 ctirvata. 



a. Upper valve. 



b. Lower valve. 



c. Frustule. 



Valves cuneate, dissimilar ; the upper valve 

 having only apseudo raphe, and without nodules ; 

 the lower valve furnished with a true raphe and 

 nodules. Frustules flexed in girdle view. En- 

 dochrome as in the Gomphonema. 



ANALYSIS OF SPECIES. 



( Frustule from 2 to 5 c.d.m. Striae not marginal 



( Frustule 1 c.d.m. or more. Striae submarginal on upper valve . 



R. curvata. 



R. Van Heurckii. 



R. curvata (Kutz.) Grun. (Novara, p. 8 ; U.v.H. Atl, pi. 26, 

 f. 1, 2, and 3*; Type No. 224), plate 7, fig. 319. 



Valves cuneate, with upper apex slightly produced obtuse, lower moiety 

 very slightly attenuate to a sub-obtuse point, showing a lumen at each of the 

 apices. Upper valve with stria; parallel, robust, all reaching to the pseud o 

 raphe, 10 in 1 e.d.m. Lower valve with stria; radiate, about 12 in 1 c.d.m. 

 Raphe surrounded by a small hyaline zone, dilated round the central nodule. 

 Length, 1*3 to 4*5 c.d.m. 



Fresh water. Common. 



