68 BRITISH DIATOMACEjE. 



ever, enable him to discriminate between the two, even when the 

 frond of Encyonema was absent; as the terminal nodules of the 

 median line in Cymbella are placed at the extremities of the valves, 

 while in Encyonema they are removed to some distance above, and 

 occupy a place nearer the central nodule of the valve. 



The frond of Encyonema is distinctly tubular, and the frustules, 

 which are usually in single file, except towards the extremities, where 

 they are somewhat crowded, may often be seen to move to and fro 

 in the interior, unimpeded by the mucus, which in Schizonema and 

 other allied genera ordinarily retains them in a fixed position. I 

 have detected conjugation in E. prostratum. 



] . Encyonema prostratum, Ralfs. Frond nearly simple, erect or 

 prostrate. Length of filaments *2" to "5". Extremities of valve 

 rounded ; strife 18 in -001". Length of frustule -0016" to -0024". 

 Breadth of valve '0009". v.v. 



/3. One or both extremities produced. 



Ralfs, Ann. ser. 1. vol. 16. pi. iii. 3. Hass. Alg. c. 10. Prit. Anim.xvii. 22. 

 Raben. Siissw. Diat. vii. 1. Monema prostratum, Berk. Brit. Algae, iv. 3. 

 Schizonema prostratum, Grev. B. F. p. 414. Var. /3. Encyonema para- 

 doxum, Kiitz. Bacill. xxii. 1 ; Sp. Alg. p. 61. 



Fresh water. Streams or cascades, not uncommon in the spring and summer. 

 River Frome, Dorsetshire, June 1848 ; Plumpton, Sussex, April 1852, W.Sm. 

 Near Glasgow, Oct. 1853 ; Rosthern Mere, Cheshire, Aug. 1855, Br. Arnott. 

 Lancaster, Nov. 1853 and July 1854, Mr. Johnson. Hornby, Lancashire, 

 May 1853, Mr. G. S?nith. Surrey, Mr. Capron. Var. /3. Penzance, Nov. 

 1852, Mr. Ralfs. Plumpton, April 1852, W.Sm. (Chaudfontaine, Belgium, 

 June 1851 ; Canal du Midi, South of France, May 1854, W. 8m.) 



Plate LIV. 345. Sporangial frustule? 345 a, sp. Var. (3. 345/3. a' & a". 



2. Encyonema caespitosum, Kutz. Frond often much divided at 

 summit, erect, tufted. Length of filaments '2" to *5" ; extremities 

 of valve somewhat attenuated, obtuse ; striae 24 in *00l". Length 

 of frustule -0009" to -0014". Breadth of valve -0005". v.v. 



/3. One or both extremities of valve produced. 



Kutz. Sp. Alg. p. 61 ? Raben. Siissw. Diat. vii. 5. Encyonema prostratum, 

 Kiitz. Bacill. xxv. 7. 



Fresh water: lakes or streams. Plumpton Pond, Sussex, April 1852; 



