408 DIATOMACE^. 



vexity in the end view, and the different character of the 

 marginal stride. Owing to the frustules being convex, not 

 merely in thickness, but having rounded extremities, the 

 strias are evident on a portion of the front surface. 



The species grows most luxuriantly in gently running 

 water, frequently investing Cladophora glomeraia, and causing 

 it to appear of a deep brown or chocolate colour. It is at- 

 tached to this plant by means of a stipes, first detected by 

 Mr. Jenner, the existence of which from its locality in flow- 

 ing water might have been predicted. 



In drying it changes to a greenish hue. 



2. DiATOMA ELONGATUM Ag. 



Plate XCIV. Figs. 3, 4, 5, 6. 



Char. Frustules many times as hroad as long, at first with 

 straight margins^ subsequently, when fully developed, the 

 sides are dilated on the front surface. End view linear, 

 with slightly incrassated ends. — -/3 cuneatum. Frustules 

 wedge-shaped. 



Diatoma tenue Ag., Consp. Diatom, p. 52. Z>. tenue S 

 normale Klitz., in Linnaea, 1838, p. 580. t. 17. f. 63. D. 

 elongatum Berk., Glean, t. 6. ; Hook. Br. Fl. 406. ; Harv. 

 Manual, p. 202. D. sulphurascens Ag., Consp. Diatom, 

 p. 53. Conf. flocculosa Dillw., Br. Conf. t. 28. f. C. ? 

 Bacillaria pectinalis Ehr., Infus. p. 198. pi. xv. fig. 4. in 

 part only. D. elongatum Ag., Syst. p. 4. ; Klitz. in Lin- 

 naea, p. 582. t. 17. f Q5. Bacillaria elongata Ehr., In- 

 fus. p. 218. f. 169. D. tenue and D. elongatum Ralfs, 

 in Annals, vol. xi. p. 451, 452. pi. ix. fig. 1. ; Z). tenue 

 Jenner, loc. cit. p. 202. Bacillaria cuneata Ehr., Infus. 

 t. XV. fig. 6. Diatoma tenue y cuneatum Klitz., in Lin- 

 naia, 1833, p. 580. t. 17. fig. 62. 



Ilab. Pools and streams. Near Tunbridge Wells : 3Ir. 

 Jenner. ^hrewshurj : 3Ir. Leighton. Cheshunt: A. H. H. 

 Bangor, and Dolgelly, North AValcs ; Penzance: Mr. 



