DIATOMA. 407 



1. DiATOMA VULGARE Bory. 



Plate XCIV. Figs. 1, 2. 



Char, Frustules two or three times broader than long, some- 

 times attached hy a stipes. Lateral puncta very evident. 

 End view hiflated, incrassated at tlie terminations, and 

 striated. 

 Diatoma vidgare Kiitzing, in Linnaea, 1833, p. 582. f. M. 

 D. tenue Grev., Crypt. Fl. t. 354. ; Berk. Brit. Alg. 

 L 6. ? Hook. Br. Fl. vii. p. 406. ; Harv. Manual of Br. 

 Algag, p. 202. D. tenue a moniliforjne (Young) Kiitz., 

 in Linngea, 1833, p. 580. f. 60.? D. tenue jS interme- 

 dium Kiitz., 1. c. p. 580. f. 61.? D. flocculosum Ag., 

 Consp. Crit. Diatom, p. 53. excl. syn. Dillw. Bacil- 

 laria vulgaris Elir., Die Infus. p. 197. pi. 15. f. 2, 

 Diatoma vulgare Balfs, in Annals, vol. xi. p. 450. pi. viii. 

 fig. 8. ; Jenner, in FL of Tunbridge Wells, p. 202. 



Hah. Pools, streams, &e. King's Cliff, Northampton- 

 shire : Rev, M. J. Berkeley. Henfield, Sussex : Mr. 

 Borrer, Shoreham, Kent, and several stations about 

 Lewes and Tunbridge Wells : Mr. Jenner. Shrewsbury : 

 Mr. Leighton. Oswestry, Shropshire : Rev. T. Salwey. 

 Cheshunt, Herts : A. H. H. Ireland : Mr. D. Moore. 



This species, like most of the Diatomacece, varies very con- 

 siderably in the length and breadth of the frustule, as well as 

 in the degree of its convexity. Usually each frustule is about 

 two and a half times as broad as long ; in this state the frus- 

 tules are seen to be very convex in the end view, but some- 

 times older specimens are met with, in which the breadth of 

 the frustules exceeds some ^yq or six times their length, and 

 in this they are scarcely at all convex when viewed endways. 

 This condition of the species might almost mislead one to re- 

 gard it as a distinct species. See the figures. 



From Diatoma tenue, or rather D. elongatum, of which 

 D. tenue is but a state, with which, however, there is but 

 little danger of confounding it, D. vulgare may be distin- 

 guished by the greater breadth of the frustules, their con- 



D D 4 



