EUNOTIA. 299 



2. Frtistules not united in filaments (true EUNOTIA). 



f Valve of medium or small size, with fine striae, and dor- 

 sum not indented - . . . E. Vensris. 



Valve very small and very narow, with three slight 



elevations . . . . E. tridentula. 



( Strife very distant in the median portion . E. piasrupta. 



free not Valve I St,1<ne ver y delicate dorsum with two 



tree not j xrme r idges .... E. bidentula. 



parasitic on large and ft *. 



other plants. , robust, - 0t . jr. 1 



c , , 1 Striae very delicate, dorsum 



dorsum "' Strins with three rid S es E triodon. 



level or approxi- 



furnished 



mate. j Striae robust, dorsum with 



withstrong ! ^ more than three ridses ' E ' robusta - 



ridges. 



I Striae robust, dorsum with two slight 



L ridges . . . . E. diodon. 



,-, , 1 Valve very long, robust, straight or flexuous, with apices 



ic U f inflated . . . . . E. flexuosa. 



parasitic 



on other 

 plants. 



Valve rather small, narrow, arcuate, with apices some- 

 times rostrate-capitate, not inflated . . E. lunaris. 



I. Frustules united in filaments of greater or less length. 



(HlMANTIDIUM OF AUTHORS). 



a. Apices of valves reflexed on the dorsal margin. Individuals forming 



short filaments. 



E. ArCUS Ehr. (AM., 1840, p. 17 ; Inf., pi. 21, f. 22 ; H.V.H. Atl., 

 pi. 34, f. 2* ; Type No. 267 a form approximating to var. uncinata ; Type 

 No. 268, forma curta), plate 9, fig. 362. 



Valve arcuate, with apices strongly capitate, ventral margin straight or 

 slightly arcuate ; striae delicate, about 12 in 1 c.d.m., finely divided trans- 

 versely. Girdle face rectangular-linear-elongate, connecting zone with very 

 fine transverse striee (22 in 1 c.d.m.), interrupted by longitudinal plicae. 

 Length, 3 to 9 c.d.m. 



Fresh water. Rare? Belonging to calcareous regions according to Grunow. England 

 (Comber, Kitton, Norman), Scotland (Dickie), Ireland (O'Meara). Found throughout Europe. 



var. minor. (H.V.H. Atl., pi. 34, f. 3*), plate 9, fig. 363. 

 Smaller (about 3 cd.m.) and more slender. 



var. uncinata. (H.V.H. Atl., pi. 34, f. 13*), plate 9, fig. 364. 

 Dorsal and ventral curvatures strong. 



var. bidens. (H.V.H. Atl., pi. 34, f. 7*), plate 9, fig. 365. 

 Dorsal margin showing two slight gibbous ridges. 



Mixed with the type form. 



