58 BRITISH DIATOMACEiE. 



Sussex, September 1853. Landport, Sussex, December 1853, &c, W.Sm. 

 Aberdeenshire, November 1851, Dr. Dickie. (Vaucluse, Le Puy, Puy de 

 Dome, Source of the Loiret near Orleans, and Champs Elysees, Paris, 1854, 

 W. Sm.) 



The only species with which this universally distributed form can be con- 

 founded is the last ; but from this a careful examination will enable the 

 observer to separate it. M. varians has the extremities of its frustules 

 closely applied and partially truncate ; those of M. subflexilis are often more 

 or less separated by a mucous cushion, and distinctly convex. The latter 

 species has never occurred to me except in water under marine influences. 

 M. varians is found in every clear spring and river, from the lowest to the 

 most elevated situations. M. subflexilis, when found in abundance, appears 

 as a dark green iridescent mass. M. varians always presents a rich golden- 

 yellow or chestnut hue to the eye. The geminate arrangement of the frustules 

 is conspicuous in M. subflexilis, and indistinct in M. varians. The two 

 species have been often confounded, but I think the differences they present 

 are quite sufficient to warrant their separation. 



Plate LI. 332. 



5. Melosira nivalis, n. sp. Frustules subcylindrical ; valves sub- 

 hemispherical, distinctly cellulate; cellules circular; extremities 

 of valves more or less truncate. Breadth of filament '0002" to 

 •0007". v.v. 



Fresh water : alpine pools. Snow mud, Ben M c Dhui, elev. 2800 feet, Dr. 

 Dickie. Pass of Killiecrankie, August 1854, Dr. Greville. Mull Deposit, 

 Dr. Gregory. (Pic de Sancy, elev. 6000 feet, June 1854, W. Sm.) 



The present species hardly differs from the next except in the greater 

 distinctness of the cellules, a character probably insufficient to justify their 

 separation. 



Plate LIII. 336. 



6. Melosira distans, Kutz. Frustules subglobular; valves sub- 

 hemispherical, obscurely cellulate. Breadth of filament •0002" to 

 •0009". v.v. 



Kutz. Bacill. ii. 12. Gallionella distans, Ehr. Microg. tab. xv. F. ad speci- 

 mina authentica. 



Freshwater. Elgin, August 1854, Dr. Gregory. Braemar, August 1854, 

 Dr. Balfour. (Puy du Capuchin, Mont Dore, elev. 4567 feet, June 1854, 

 W. Sm.) 



Plate LXI. 385. 



