406 DIATOMACE^. 



Diatoma fenestratum Lyngb., Hydr. Dan. t. 61. E. 3. ; 

 Ag. Consp. Diatom, p. 53. ; Hook. Br. Fl. vol. vii. 

 p. 406. ; Harv. Br. Alg. p. 202. ; Kalfs, in Annals, 

 vol. xi. p. 453. pi. ix. fig. 4. ; Jenner, in Flora of Tun- 

 bridge Wells, p. 200. 



Hab. Pools, &c. ; Sussex, &c. : Mr. Jenner. Cheshunt : 

 A. H. H. Barmouth, North Wales : Rev. T. Salwey. 

 Dolgelly, and near Pont-Aberghas-lyn, North Wales, 

 and Penzance : BIr. Rolfs. Stevenston, Ayrshire : Rev. 

 D. Landshorough. Aberdeen ; Dr. Dickie. 



This is one of the least variable of the species of this and 

 the following genus ; it may however be confounded with 

 TabeUaria Jiocculosa in the last stage of its developement ; 

 but with a little care it may be readily distinguished there- 

 from. In T. fenestrata the frustules are connected by a per- 

 ceptible hinge, and on each fully developed frustule there are 

 at each extremity two stria?. In T. Jiocculosa tbe mucous 

 hinge is not visible connecting the frustules, which are usually 

 much longer, and on the narrowest, Avliich approach nearest to 

 T. fenestrata, there is frequently but a single stria at one 

 side, and two at the other. The end views of the frustules 

 in the two also differ. In T. Jiocculosa the frustule is more 

 slender, the ends less incrassated, and the canal more pro- 

 longed. 



The frustules in this species and in D. elongatum are often 

 curiously thrown back so as to form two lengthened scries. 



70. DIATOMA Ag. 



Char. Frustules not having a central canal or lateral stricB, 

 punctated at the sides, the puncta being produced by the 

 presence of grooves, which pass round the frustules. Junc- 

 tion surfaces often striated. 



Derivation. From hiaroixri, ijicision ; the plant looking like 

 a band cut into portions, which cohere only at the 

 angles. 



