BRITISH DESMIDIE^. 145 



13. TETMEMORUS, Ralfs. 



Frond simple, elongated, straight, cylindrical or fusiform, slightly 



constricted at the middle ; segments emarginate at the end, but 



otherwise quite entire. 



The frond is elongated, as in Penium, from which however this genus 

 may be distinguished by the emarginate ends ; the same character and 

 the elongated frond will separate it from Cosmarium. 



From Euastrum, with which it agrees in the emarginate extremities, 

 it differs in being cylindrical or nearly so, and in the segments being 

 neither lobed nor sinuated j the fronds are also free from inflated pro- 

 tuberances. 



Sporangia have been gathered of two species. 



1. T. Brebissonii (Menegh.) ; frond in the front view with parallel 

 sides, but in the lateral view fusiform ; the ends without any pro- 

 jecting processes ; puncta in longitudinal lines. 



/3. turgidus', larger, constriction greater; segments somewhat 

 inflated. 



Closterhim Brebissonii, Menegh. Syn. Desmid. in Linneea 1840, p. 236. 



Closterium (sp. 9), Bailey, Amer. Bacil. in Amer. Journal of Science and Arts, 

 vol.41, no. 2. t. 1. f. 38 (1841). 



Tetmemorus Brebissonii, Ralfs, Ann. of Nat. Hist. v. 14. t. 8. f. 1 (1844) ; 

 Trans, of Bot. Soc. of Edinburgh, v. 2. p. 133. t. 12. Jenner, Fl. of 

 Tnnbridge Wells, p. 198. Hassall, Br. Freshwater Alg. p. 377. 



Closterium monile, Kiitzing, Phycol. Germ. p. 132 (1845). 



Dolgelley ; Carmarthen ; Penzance, J. R. Sussex ; Kent ; Surrey and 

 Hants, Mr. Jenner. Many stations in Aberdeenshire (alt. 50 — 3700 feet), 

 Mr. P. Grant and Dr. Dickie. Banffshire, 3Ir. P. Grant. Ambleside, Mr. 

 Sidebotham. 



/S. Ashdown Forest, Sussex, Mr. Jenner. 



Falaise, Brebisson. Germany, Kiitzing. Maine to Virginia, Bailey. 



Frond four to six times longer than broad, with a slight constriction at the 

 middle. The front view shows the lateral margins of the segments nearly 

 straight, and their ends rounded and emarginate. The lateral view is more 

 constricted at the middle and the segments are attenuated towards the end. 



The endochrome is dark green, and there is a series of large vesicles down 

 the middle m a single row, either straight or with some irregularity. The 

 frond, when empty, is found to be minutely punctate, the puncta being ar- 

 ranged in longitudinal rows. 



The var. /3. somewhat approaches in form to Tetmemorus granulatus, but is 

 more constricted at the middle, and the puncta form longitudinal lines. 



