FRAGILARIA. 415 



Hob. In freshwater pools and rivulets, Sussex : Mr. Bor- 

 rer. Llyn Prefeddyr, near Barmouth : Rev. T. Salwey. 

 Aberdeen : Dr. Dickie. Stevenston : Rev. D. Lands- 

 borough. Ballantrae, Ayrshire : Mr. W. Thompson. Dol- 

 gelly, Tavistock, and Trenteshoe, Devonshire ; Pen- 

 zance, Cornwall : Mr. Ralfs. 



This is a smaller species than Fragilaria pectinalis, differ- 

 ing from it also in the slightly emarginate sides of the frustules, 

 the elliptico-lanceolate form of their end view, and the paucity 

 and decided character of the striae seen on the end surface. 



The filaments are so fragile, that the frustules separate on 

 the slightest touch, so that it is rare to meet with a filament 

 of any length. In most specimens the frustules are as long 

 as broad, and some even longer ; but in others, again, they are 

 two or three times broader than long. The filaments not so 

 unequal as in the other British species of the genus. When 

 recent, it is of a dark brownish colour, becoming whitish 

 brown in drying. 



There can be no doubt of the correctness of the reference 

 to Ehrenberg. 



3. FRAGILARIA RHABDOSOMA Ehr. 

 Plate XCV. Fig. 6. 



Char. Filaments much compressed. Frustules usually many 

 times broader than long ; in the end view lanceolate, and 

 without strice. 



Ehr. Die Infus. p. 204. t. 15. f. 12. Frag, pectinalis 

 Kiitz., in Linnaea, 1833, p. 73. ? Frag, tenuis Ag., Con- 

 spect. Diatom, p. 63. ? Ralfs, in 1. c. p. 108. pi. xi. fig. 4. 

 F. bipunctata, F. angusta, F. scalaris, and F. diopthalma 

 Ehr., t. xv. F. rhabdosoma Jenner, in Flora of Tun- 

 bridge Wells, p. 202. 



Hob. Common in pools and ditches. 



The exceedingly narrow frustules, and the lanceolate form 



