148 



ENCYONEMA. 



C. tumida Breb (Cocconema tumidum Brcb. ! in Kutz Sp. Alg., 

 p. 6c, 11. 5 ; H.V.H., pi. 2, f. 10*; Type No. 21), plate 1, fig. 42. 



Valves ventricose, with dorsal margin very arcuate, ventral margin 

 concave, inflated in the middle, apices very produced-rostrate, truncate or 

 rounded. Raphe very arcuate, surrounded by a rather broad hyaline zone, 

 very considerably inflated round the central nodule, dilated portion some- 

 times showing one or two isolated granules ; central nodule generally having 

 a small furrow across it in the middle ; stria; robust, quite moniliform, 8 to 9 

 in 1 c.d.m. Length, about 6 c.d.m. Frustule stipitate. 



Fresh or slightly brackish water. Antwerp, Louvain, Ostend, etc. 

 Terminal nodules very elongate 



C. Helvetica Kutz. ! (Baa, p. 79, pi. 6, f. 13; h.v.h. Atl., 



pi. 2, f. 15*; Type No. 32); plate 1, fig. 43. 



Valve very lanceolate, with dorsal margin rather convex, ventral margin 

 very slightly concave, almost straight, abruptly inflated in just the middle 

 portion ; raphe slightly bent, with curvature inflected at the middle of the 

 valve towards the ventral margin \ raphe surrounded by a narrow hyaline zone, 

 slightly inflated near the central nodule ; terminal nodules very long, in the 

 form of a coarse inverted comma ; stria; rather well marked, divided cross- 

 wise, about 8 to 9 in 1 c.d.m. Mean length about 7 c.d.m. 



Fresh water. Very common, and found in all the countries comprised within our radius. 



GENUS 3. ENCYONEMA KUTZ., 1833. 



Fig. 27. Encyonema prostration (Berk.) Ralfs, 



