Prof. W. Smith on the Diatomacese of the Pyrenees. 1 1 



Cost^ distant, 10 in -001". Length of frustule -00] 3" to 

 •0036". Breadth of valve -0001". v.v. 



Marine. Very rare in rocky pools near Biarritz. 



I am uncertain as to the true position of the above form : the 

 filaments are direct as in Fragilaria, the frustules arcuate as in 

 Himantidium, and the valves costate as in Meridion. As the 

 second character seems the most important in the present case, 

 I have placed the species provisionally in Himantidium, but a 

 further and better knowledge of its habit and character may 

 necessitate the adoption of a new generic appellation. 



Plate II. fig. 14. Himantidium marinum : a, S. V. of frustule j by F. V. of 

 filament. 



Melosira cribrosa, Breb. S. V. orbicular, cellulate ; cellules all 

 equal and hexagonal, 9 in 'OOl". Diameter of valve '0025". 



v.s. 



Marine. Bay of Biscay near Biarritz. 



In December 1853 I received isolated frustules of this species, 

 collected on the coast of Normandy, under the above name from 

 M. de Brebisson, and I have since detected the same in a 

 gathering from the Black Sea. In no case have I seen the 

 frustules in a recent state, and do not know whether they ever 

 form a lengthened filament. As this is the only circumstance 

 that would justify their separation from Coscinodiscus, to which 

 the separated valve would otherwise seem to belong (see Synop. 

 B. Diatomacese, vol. i. p. 23), their position in Melosira must 

 rest upon the authority of my accurate correspondent. 



Plate II. fig. 15. S. V. oi Melosira cribrosa. 



Genus Diadesmis, Kiitz. 



Frustules naviculoid, united into a free or attached filament ; 

 valves elliptical with a median line, and central and terminal 

 nodules. 



Diadesmis Gallica, n. sp. Filaments direct or curved. S. V. 

 linear-elliptical. Striae obscure, about 45 in "OOl". Width 

 of filament -0003'' to -0004". Breadth of valve -0001". v.v. 



Fresh water. Fountain in the court of the Hotel Frascati at 

 Havre. 



The genus Diadesmis is not without an illustrative species in 

 the British Islands, though the habitat of this species makes it 

 doubtful whether it be really entitled to rank as indigenous. It 

 was collected by Dr. Arnott in the tank of the Victoria Regia at 



