Mr. J. Ralfs on the Diatoniaceae. 453 



of the normal form or dilated at the opposite end. In one chain 



I perceived in miion fonr frustules thus formed, which answers to 



the description of BaciUaria cuneata, Eh., but the frustules were 



longer than in Pritchard, f. 170, or in Kutzing. 



I subjoin Ehrenberg's specific character of BaciUaria cuneata: — 

 " BaciUaria striata, testula pyramidali cuneata, truncata subqua- 



drata, alternis apicibus dilatatis, intus Isete flavo-viridis, p. 198. pi. 15. 



f. G. Diatoma tenue, y, cuneatum, Kutz. in Linnsea 1833, p. 580. 



t. 17. f. 62." 



I am also informed by Mr. Dalrymple that Ehrenberg states 

 that " this characteristic little form is apt to be overlooked, and 

 not unfrequently taken for BaciUaria pectinaUs {Diatoma tenue) ." 



** The front surface with two or more stria, interrupted in the centre 

 by a canal; lateral surf aces loithout stria. (Tabellaria.) 



4. D. focctilosum, Ag. Frustules varying from square to twice as 

 long as broad ; striee three to seven ; canal inflated. Diatoma foe- 

 culosiim, Ag. Syst. p. 4; Kutz. in Linnfca 1833, p. 584. t. 17. 

 f. 67 ; Hook. Br. Fl. v. ii. p. 406 ; Harv. Br. Alg. p. 202. Conf. 

 Jlocculosa, Dillw. Conf. t. 28. ; Eng. Bot. 1. 1761. BaciUaria tabel- 



laris, Ehrenb. Infusoria, p. 199. pi. 15. f. 7; Pritch. Infusoria, 



p. 218. 



Plate IX. fig. 3. a, common form ; b, side view ; c, end view. 



Common in pools, rivulets, &c. 



Frustules generally a little longer than broad, often nearly equal 

 in length and breadth, sometimes twice as long as broad. The 

 strife are generally five or six, in the narrower specimens only 

 three. The inflated canal is much broader than the incrassated 

 ends. It is bro^ai when recent, whitish when dry. 



Mr. Borrer considers the plant figured in ' Eng. Bot.' as di- 

 stinct from that figured by Dillwyn. The chief difference appears 

 to be, that in the front view the inflated canal and incrassated ends 

 are more strongly marked in the latter. I have gathered near 

 Swansea specimens exactly resembling Mr, Dilhvyn's fig., but I 

 am unable to find any good specific difference between them and 

 the ' Eng. Bot.' plant, and after they were diied I could perceive 

 no distinction. 



5. D.fenestrutiim, Lyngb. Frustules four times or more longer than 

 broad ; canal inflated ; strise two. D.fenestratum, Lyngb. Hydr. 

 Dan. t. 61. E. 3 ; Ag. Consp. Diatom, p. 53 ; Hook. Br. FI. v. ii. 

 p. 406 ; Harv. Br. Alg. p. 202. 



Plate IX. fig. 4. a, front view; h, side view. 



Pools and rivulets. Sussex, Mr. Jenner; Cheshunt, Mr.Hassall; 

 Barmouth, N.Wales, Rev. 2\ Salwey ; Dolgelley and near Pont-Aber- 

 glas-lyn, N. Wales, and Penzance, Cornwall. 



This species varies much in the length of its frustules. The 



