FRUSTULTA. 



437 



84. AULACOCYSTIS Hass. 

 Char. Frustules jiroduced, longitudinally sulcated. 

 Derivation. From avka^^ a groove, and Kuans, a cell. 



1. AULACOCYSTIS PELLUCIDA Hass. 



Plate CII. Fig. 8. 



Char. Frustules elongated, narroio, attenuated at each extre- 

 mity. 



Navicula? pellucida, Die Infus. p. 176. t. xiii. fig. 3. 

 Frustulia pellucida Kiitz., in Linuajn, 1833, p. 543. 

 t. xiii. fig. 11.; Jenner, in Fl. of Tunbridgc Wells, 

 p. 204. 



Ilab. Ashdown Forest, and at Shoreliam, Kent; between 

 Tunbridge Wells and the High Rocks : il/r. Je7mer. 



There can be no doubt of the propriety of separating this 

 species from the genus Navicula of Ehrenberg. 



85. FRUSTULIA Kiltz. 



Cliar. Frustules elongated, quadrangxdar, with tico longitudinal 

 grooves and two central depressions. 

 Derivation. Yvom frustuhan, a small fragment. 



I must confess that 1 do not exactly understand the struc- 

 ture of the single species which I propose to retain in the 

 genus Frustidia. It is possible that to this genus should be 

 referred those species of Navicida which have striated frus- 

 tules ; and, if not to this genus, possibly those species should 

 be regarded as Cymhellce. 



1. Frustulia? \iuit>i^ Kutz. 



Plate CII. Fig. 2. 



Char. Frustules large, elongated. In front view quadrangu- 

 lar, with straight sides and truncate extremities ; laterally 

 slightly infiatcd in the centre, with rounded ends. 



F F 3 



