TETMEMORUS. 377 



part of considerable size do not require for their satisfactory 

 examination the high and delicate powers with which most of 

 the DesmidecB need to be examined. 



60. TETMEMORUS Ralfs. 



Char. Frond elongated, straigM, suhcylindrical, slightly con- 

 stricted in the centre. Segments emarginate at their ex- 

 tremities but otherwise entire, being neither lobed nor 

 sinuated. 



Derivation. From ts/jlvco, to cut. 



The two species for the reception of which this genus has 

 been created are placed by Meneghini in the genus Closterium 

 with the other species of which they do not well accord. 



From Closterium it differs in the emarginate extremities of 

 the segments, and in the absence of the cells containing the 

 revolving particles : from Cosmarium it is separated by the 

 divided segments, as well as by its elongated fronds. 



From Euastrum, with which it agrees in the terminal 

 division of the segments, it differs in being neither lobed nor 

 sinuated. 



1. Tetmemorus Brebissoni Ralfs. 

 Plate LXXXIX. Fig. 5. 



Char. Frond about Jive times as long as broad, considerably 

 constricted in the centre. Segments in the front view 

 somewhat quadriform, but in the lateral view attenuated, 

 longitudinally striated. Granules in a j^oio down the 

 centre of the frond. 



Closterium Brebissoni Menegh., Syn. Desmid. in Linnjea, 

 1840, p. 236. Closterium (sp. 9.) Bailey, American 

 Bacillaria, in Amer. Jour, of Science and Arts, vol. xli. 

 No. 2. pi. i. fig. 38. Tetmemorus Brebissoni Ralfs, 

 Ann. vol. xiv. p. 258. pi. viii. fig. 1. ; Jenner, in Flora 

 of Tunbridge Wells, p. 198. 



