/» BRITISH DIATOMACEiE. 



the genera which have preceded it, and the presence of nodules in 

 its valves from Podosphenia and Wiipidophora^ with which the pre- 

 sent genus has sometimes been confounded. The latter genera are 

 also exclusively marine, while the species of Gompjhonema, with one 

 exception (and that a species doubtfully connected with the present 

 genus), are all inhabitants of freshwater streams and ponds. The 

 same mode of branching characterizes the stipes of the present genus 

 as that noticed under the genus Cocconema ; and excluding the excep- 

 tional species just mentioned, this appendage, in the present as in that 

 genus, when fully developed, consists of an elongated dichotomous 

 filament. Conjugation and the formation of Sporangia have been 

 observed by Mr. Thwaites in G. Berkeleyi, G. tenellum, and G. curva- 

 tum ; and by myself in those species, G. capitatum and G. marinum. 



1 . Gomphonema geminatum, Ag. F. V. slightly cuneate, truncate ; 

 V. inflated at the centre and constricted towards each extremity, 

 of which the one more distant from the stipes (the upper) is enlarged 

 and rounded; striae moniliform, 24 in 'OOl". Length -0041" to 

 •0052". v.v. 



Ag. Syst. p. 12. Grev. C. F. pi. 244. fig. 2. Harv. Man. p. 207. Ralfs, 

 Ann. vol. xii. pi. xviii. 3. Hass. Alg. xcvaii. 1. Kiitz. Bacill. xiii. 2. 

 Echinella geminata, Lyng. Tent. Ixx. D. Gomp. ampidlaceum, Grev. B. F. 

 p. 410. ex specim. authen. quae communicavit cl. Dr. Greville. 



Fresh water : subalpine streams, not uncommon. Pentland Hills, Dr. 

 GrevUle. Dolgelly, Mr. Ralfs. Wray, Lancashire, 3Ir. G. Smith. Ben 

 M*^ Dhui, Mr. P. Grant. Aberdeenshire, Dr. Dickie. Lough Mourne De- 

 posit. Dolgelly Earth. 



Plate XXVIL 23,5. Frustules with endochrome, Frontispiece, fig. CCXXXV, 



2. Gomphonema constrictum, Ehr. F.V. distinctly cuneate; upper 

 extremity rounded, lower obtuse ; V. more or less constricted to- 

 wards the upper extremity, attenuated below; striae 27 in "OOl". 

 Length -0012" to -0024". v.v. 



Kiitz. Bacill. xiii. 4. Gomp. truncatum, Ehr. Inf. xviii. 1. Hass. Alg. xcviii. 2. 

 Gomp. i>ohli(eforme, Ralfs, Ann. vol. xii. pi. xviii. 4. Gomp. yeminatum, 

 Quek. H. C. xii. 4. 



Freshwater: frequent. Lewes, May 1850, &c., JT^^. &«. Harrison's Rocks, 

 Sussex, Mr. Jenner. Lough Mourne Deposit. Peterhead Deposit. Dol- 

 gelly Earth, &c. 



Plate XXVIII. 230. 



