408 DIATOMACE^. 



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

 marginal strite. Owing to the frustules being convex, not 

 merely in thickness, but having rounded extremities, the 

 stride 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. 



Cliar. Frustules 77umy times as hroad as long, at first ivith 

 straight margins, suhsequentlg, xolien fully developed, the 

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

 with slightly incrassated ends. — /3 cuneatum. Frustules 

 iDedge-shaped. 



Diatoma tenue Ag., Consp. Diatom, p. 52. D, tenue B 

 7iormale Kiitz., in Linnfea, 1838, p. 580. t. 17. f. 63. D. 

 eloJigatumBevk., Glean, t. 6.; Hook. Br. Fl. 406.; Harv. 

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

 p. 53. Co7if. focculosa Dillw., Br. Conf t. 28. f. c. ? 

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

 part only. Z>. elongatiim Ag., Syst. p. 4. ; Kiitz. in Lin- 

 na?a, p. 582. t. 17. f. &5. Bacillaria elongata Ehr., In- 

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

 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 Kiitz., in Lin- 

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



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

 Jenner. Shrewsbury: Mr.Leighton. Cheshunt: ^. i/. iZ 

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



