EUNOTIA. 303 



In all these gatherings the form is considerably shorter, more squat, with 

 ridges more elevated and more acute than in the figure in the Atlas, which is 

 5 c.d.m. It is always rare in gatherings, and is found in company with 

 JVaz\ serians, Vanh. rhomboides, etc. 



E. robusta Ralfs. (in Pritch., p. 763 ; H.V.H. Atl., pi. 33, f. 



11-13* in Types Nos. 263 and 274), plate 9, fig. 381. 



Valves robust, semi-lunar, with apices broadly rounded ; ventral margin 

 concave ; dorsum inflated, convex, with three to five ridges ; striae radiant, 

 robust, about 10 in 1 c.d.m. in the middle of the valve, many between them 

 simply marginal ; girdle face quadrangular. 



Fresh water. England, France, Sweden. 



var. tetraodon. (H.V.H. Atl., pi. 33, f. 11* ; in Types No. 51, 263, 

 462), plate 9, fig. 382. 



Dorsum with four ridges. Length, about 5 c.d.m. 



Freshwater. Liresse (Delogne). Ard. Lieg. (De Wild.). Scotland. England (Norman). 

 Ireland (O'Meara), 



E. triodon Ehr. (Inf., p. 192, pi. 21, f. 24; H.V.H. Atl., pi. 33, f. 



9 and 10* ; Type No. 263), plate 9, fig. 383. 



Differs from the preceding sp3cies by the dorsal margin, which has only 

 three ridges, and by the very delicate strue, about 16 in i c d.m., finely 

 punctate. Length, about 4 c.d.m. 



Fresh water. Ard. Lieg. (De Wild.). Scotland (Baxter Coll., No. 2633), Sweden. 



E. diodon Ehr. (inf., p. 192, pi. 21, f. 23; h.v.h. Atl., pi. 33, f. 



5, 6*), plate 30, fig. 829, 830. 



Valve with ventral margin concave, dorsal margin showing two slight 

 rounded ridges. Apices obtuse, rounded, subcapitate. Length, 5 to 7 c.d.m. 

 Breadth at the median constriction, 1 c.d.m. 



Fresh water. England, Scotland (Baxter Coll., No. 2633), Ireland (O'Meara). Fossil. 

 Sweden, Finland. 



aa. Frustules parasitic on other plants. 



E. lunaris (Ehr.) Grun. {Synedra Ehr., Infus., pi. 17, f. 4; 

 H.V.H. Atl., pi. 35, f. 3, 4 and 6A* ; Type No. 272), plate 9, fig. 384. 



Valve more or less arcuate, narrow, with apices sometimes gently rostrate- 

 capitate, not inflated, with well-marked nodules ; striae delicate, distinctly 

 punctate, 15 in 1 c.d.m. Girdle lace linear, narrow, with apices truncate, 

 somewhat produced. Length, 5 to 9 c.d.m. 



Fresh water. Rather frequent. 



