South of France and the Aarcryne. 7 



Length of frustnle -0017" to -0038". BrcaJtii of valve 

 •00025" to -0003". v.v. 



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

 cashire, April 18 18, Mr. G. Stnith. River Shannon near Athlone, 

 and Longh Corrib river, July 1853, Jr. Sm. Lough Neagh, Dr. 

 Dickie. Lough Leven, May 1851, Dr. Greyonj. 



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

 13acill. xvii. 17, but distinguished by the linear outline of its 

 valve, its closer stride, and greater relative size. 



Plate L fig. 6. Diatoma grande. 



Fragilaria undata, W. Sm. Filaments imperfectly tenacious; 

 frustules frequently cohering by their angles; valve oval or 

 linear, acuminate. Stria3 42 in "OOl". Length of frustule 

 •OOOG" to 0008". 



Var. /8. 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 Tubellaria, " sporangia," Greg. jMic. Journ. 



vol. ii. pi. A. 22. 



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

 40G(j 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 

 Frr/ffilaria. Its mode of growth and delicately striated valves 

 ally it closely with F. viresceiis. 



Plate I. fig. 7. FrcKjilaria undata. 



Oduntidium 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. /S. 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 modirication 

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



Plate L fi?. 8. Odontidium anomalum. 



