South of France and the Auvej-gne, 7 



Length of frustule -0017'' to -0038". Breadth of valve 

 •00025" to •0003'^ v.v. 



Fresh water. River Sorgues near Vaucluse ; River Lune, Lan- 

 cashire, April 1848, Mr. G. Smith. River Shannon near Athlone, 

 and Lough Corrib river, July 1853, W. Sm. Lough Neagh, Dr. 

 Dickie. Lough Leven, May 1854, Dr. Gregory. 



A very fine and distinct species allied to D. Ehrenbergii, Kiitz. 

 Bacill. xvii. 17, but distinguished by the linear outline of its 

 valve, its closer stride, and greater relative size. 



Plate I. fig. 6. Diatoma grande. 



Fragilaria undata, W. Sm. Filaments imperfectly tenacious; 

 frustules frequently cohering by their angles ; valve oval or 

 linear, acuminate. Strise 42 in -001". Length of frustule 

 •0006" to 0008". 



Var. p. Valve linear, acuminate. Length of frustule •OOOS" to 



•0012". v.v. 

 Var. y. Valve constricted in the centre. Length of frustule 



•0008" to -0021". v.v. 

 Var. y. Odontidium Tabellaria, " sporangia," Greg. Mic. Journ. 



vol. ii. pi. 4. 22. 



Fresh water. River Mortes, Lac Guery, Mont Dore ; elevation 

 406G feet. Var. y. Mull Deposit, &c. 



The specimens which I collected in the locality above men- 

 tioned enabled me to assign the present species to the genus 

 Fragilaria. Its mode of growth and delicately striated valves 

 ally it closely with F. virescens. 



Plate I. tig. 7- Fragilaria undata. 



Odontidium anomalum, W. Sm. Filament tenacious ; valves 

 linear, constricted towards the obtuse extremities. Costse 4 

 to 12. Length of frustule -0005" to -0012". v.v. 



Var. p. Frustules with internal cells. 



Fresh water. Genolhac in the Cevennes ; elevation about 4000 ft. 

 Braemar, Perthshire, Aug. 1854, Dr. Balfour. 



The presence of internal cells within the ordinary frustule, a 

 mode of growth occasional in others of the Diatomacese, is fre- 

 quent in this species, and frustules of the more usual descrip- 

 tion are rarely to be detected in the above gatherings ; they may 

 however be found at times, side by side with others, containing 

 internal cells, showing that the latter formation is a modiHcation 

 of the usual method, and not a normal condition of the filament. 



Plate I. fi}'. 8. Odontidium anomalum. 



