ACHNANTHES. 



277 



true raphe and nodules. Frustules geniculate in girdle view, solitary 

 or united by threes. 



This genus, with the character above given, only embraces a single species. 



A. flexellum Breb. (in Kiitz. Spec. Alg., p. 54; H.V.H. Atl., 

 pi. 26, f. 20, 30, 31*), plate 8, fig. 322. 



Characteristics of the genus. Striae radiate, delicate, finely punctate, 1 7 

 in 1 c.d.m., the median alternately long and shoit, more distant and more 

 strongly marked. Length. 4 to 5 c.d.m. 



Freshwater. Rare. Bergh (Delogne). Env of Louvain (H.V.H.) England (Comber, 

 Kitton), Scotland. Ireland. 



GENUS 30. ACHNANTHES BORY., 1822. 



Valves naviculoid, dissimilar, with straight raphe. Upper valve 

 with only a pseudo raphe, and without nodules ; lower valve with true 



m 



t:::::U:;:::J 



feilU 5 



a b. c. 



1'ig 61. .Achnanthes brevipes. 



a. Upper valve. 



b. Lower valve. 



c. Frustule. 



raphe, and central and terminal nodules. Frustules geniculate in 

 girdle view ; individuals solitary, geminate, or united into bands. 

 Endochrome formed of a single layer, very thick, resting on the 

 internal surface of one of the two valves, so that the other remains 

 fiee. 



