DIATOMA. 407 



1. DIATOMA VULGARE Bory. 

 Plate XCIV. Figs. 1, 2. 



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

 times attached by a stipes. Lateral puncta very evident. 

 End view inflated, incrassated at the terminations, and 

 striated. 



Diatoma vulgare Kiitzing, in Linnaaa, 1833, p. 582. f. 66. 

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

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

 Algae, p. 202. D. tenue a moniliforme (Young) Kiitz., 

 in Linnaea, 1833, p. 580. f. 60.? D. tenue (3 interme- 

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

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

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

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

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



Hob. Pools, streams, &c. 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 five 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 



