240 VANHEURCKIA. 



I. Stria quite parallel: Eu-Vanheurckia. 



V. rhomboides Breb. ! (Monog. genus Vanheurckia, p. 204 in 

 An. Soc. Phyt. et Mic. de Belg. j H.V.H. Atl., pi. 17, f. 1 and 2* ; Type No. 

 t6o), plate 5, fig. 249. 



Valves rhomboidal-lanceolate, attenuate and slightly constricted towards 

 the apices. Raphe double, with threads approximate, continuous. Transverse 

 striae fine, reaching to the raphes, about 28 in 1 c.d.m., finely moniliform ; 

 Endochrome yellowish. Length. 7 to 8 c.d.m. 



Fresh water, peat bogs. Calmpthout (Deby) Ard. Lieg. (De Wild.) England, France, etc. 



var. crassinervis. (N. Crassinervia Breb. /TV". Saxonica Rab. ; 

 H.V.H. Atl., pi. 17, f. 4 and 5 ; Type No. 162), plate 5, fig 250. 



Size smaller, about 5 c.d.m. Valve with apices more rostrate; stria; 

 very fine and very difficult to resolve, 34 to 35 in 1 c.d.m. 



V. viridula Breb. (Soc. cit., p. 203; H.V.H. Atl., pi. 17, f. 3*; 



Type No. 163), plate 5, fig. 251. 



Valves rhomboidal-elongated, attenuated with regularity as far as the 

 obtuse apices. Raphe with threads approximate, continuous. Striae fine, 

 28 to 30 in 1 c.d.m., parallel, finely moniliform. Endochrome greenish, 

 Frustules sometimes enclosed in tubes. Length, 10 to n c.d.m. 



Fresh water, Ard. Lieg. (De Wild. ). France. 



77. Median stria slightly radiant : Pseudo-V anheurckia. 

 V. vulgaris (Thwaites) H. Van Heurck. (Coiietonema 



Vulgare Thw. ; H.V.H. Atl., pi. 17, f. 6*; Type No. 164), plate 5, fig. 252. 



Valves elliptical-lanceolate, with apices obtuse, slightly contracted-rostrate. 

 Raphe double with narrow threads, then approximate and interrupted near the 

 central nodule which is surrounded by a small hyaline area. Striae fine, 

 delicate, the median striae slightly radiate, the terminal parallel, about 34 in 

 1 c.d.m. ; the median striae more robust, more distant, 24 in 1 c.d.m. and 

 more radiate. Frustules enclosed in tubes generally without branches. 

 Length, about 5 c.d.m. Breadth, about 1 c.d.m. 



Fresh water. Antwerp, Rochehaut (Delogne). Ard. Lieg. (De Wild.) England, France. 



