BRITISH DIATOMACEJE. 21 



I had the pleasure of detecting the above species during the printing of the 

 present sheets, in a gathering sent me by Dr. Gregory of Edinburgh. The 

 frustules on the F. V. closely resemble small specimens of Ephitkemia Argus, 

 but the valve is wholly different. The extremities of the costse or canaliculi 

 appear as circular foramina on the F. V., and the costee on the S. V. also 

 give an ocellated appearance to the valve, which serves to distinguish it from 

 any other species in the present genus. 



5. Denticula sinuata, n. sp. Frustule linear, truncate ; V. lanceo- 

 late, margin with three undulations; stria? delicate, 52 in '001"; 

 costae interrupted, 10 in -001". Length of frustule -0008" to 

 •0015". v.v. 



" Denticula sinuata," ad specimina sub hoc nomine cruse misit am. Thwaites, 

 Oct. 4, 1848. 



Fresh water. Near Bristol, Mr. Thwaites. Wray, Nov. 1851, Mr. Geo. 

 Smith. Killiecrankie, Mr. P. Grant. Dryburgh, March ; Pentland Hills, 

 July 1854, Br. Greville. Cumbrae Island, Feb. 1854, Mr. R. Kennedy. 



Plate XXXIV. 295. 



Genus 35. PRAGILARIA, Lyng. 



Frustules linear, straight, united into a filament, free or attached, 

 direct ; valves linear, or elliptical, direct, striated. 



The filaments of the present genus are less fragile than those of 

 any previously described, and in this respect the name, as I have 

 elsewhere remarked, has been unfortunately retained for species 

 which had better have been ranged under another appellation. In 

 fact, nothing can be more embarrassing than the changes to which 

 the various species originally described by Lyngbye under the name 

 of Fragilaria have been forced to undergo. Only one of the eight 

 species he has placed in this genus will be found below, and that one 

 has been restored to its position in opposition to the authority of 

 Professor Kutzing, who has excluded it altogether from the Dia- 

 tomaceae. 



It must be admitted that the species described by Lyngbye are 

 far too heterogeneous in their characters to be united under one 

 genus, and that their separation was imperative in the present more 

 advanced state of the science ; still it is much to be regretted that 



