My. J. Ralfs on the British Dcsmidicce. 257 



mitics, it differs in being cylindrical or nearly so, and in the seg- 

 ments being neither lobed nor sinnated ; the fronds are also free 

 from inflated protuberances. 

 Starch is found in both species. 



1 . T. Brebissonii. Segments in the front view with parallel sides, 

 but in the lateral view attenuated ; the ends without any projec- 

 ting processes. Closterium Brebissonii, Mngh. Syn. Desmid. in Lin- 



nsea 1840, p. 236. Closterium (sp. 9), Bailey, Amer. Bacil. 



in Amer. Journal of Science and Arts, vol. xli. no. 2. pi. 1. fig. 38. 

 Ashdown Forest, Warbleton, Henfield, &c., Sussex, and near Tun- 

 bridge Wells, 3fr. Jenner ; Dolgelley, Carmarthen and Penzance. 



Fronds about six times longer than broad, with a slight con- 

 striction in the middle ; the front view shows the lateral margins 

 of the segments nearly straight, with rounded and emarginatc 

 ends. The lateral view is more constricted in the middle, and 

 the segments are attenuated towards the end. 



The endochrome is dark green, and there is a scries of large 

 globules down the middle in a single row, either straight or with 

 some irregularity. 



The fronds, when emptj^, are found to be minutely punctate, 

 the puncta being arranged in longitudinal rows. 



This species differs from the following one in having its front 

 and lateral views unlike each other, and its puncta arranged in 

 longitudinal lines. 



Plate VIII. fig. 1. Tetmemorus Brebissonii : o, front view ; h, side view ; 

 c, empty frond ; d, segment. 



2. T. granulatus. Fronds tapering both in the front and lateral views, 

 and ending in a colourless projecting lip-like process. Closterium 

 granulattim, Breb. in Mngh. Synop. Desmid. p. 236. 



In boggy pools, Ashdown Forest and Henfield, Sussex ; bogs at 

 Fisher's Castle near Tunbridge "Wells, Mr. Jenner ; Dolgelley and 

 Penzance. 



Fronds cylindrical, about six times as long as broad, very 

 slightly constricted in the middle, fusiform. The extremities 

 always have a colourless projecting lip-like process which extends 

 beyond the notch. 



The colouring matter is dark green, and a few large green 

 globules are arranged in a longitudinal row down the middle. 



The empty frond is minutely punctated ; the puncta generally 

 form one or two transverse lines in each segment near the central 

 constriction, and in the other parts of the frond they are not in 

 rows, but scattered. 



Under a low power of the microscope this species much re- 

 sembles the preceding ; but it may always be distinguished by the 

 front and lateral views being similar and only differing in the 



