CONTAINING DIATOMACEOUS EXUVIAE. 1 5 



have, for the convenience of description, grouped them under 

 the name of Navicula varians, and I feel assured that the study 

 of these forms will throw much light on the question, to which 

 I have already directed attention, of the true value of form as 

 a specific character. 



I cannot conclude, for the present, without expressing the 

 very great obligations I am under to Mr. Tuffen West, not 

 only for the great care and accuracy with which he has drawn 

 and engraved the figures, but also for the valuable assistance 

 I have derived from his extensive and exact knowledge of 

 the British Diatomaceae in this long and laborious investiga- 

 tion. It is, indeed, fortunate for British microscopists that 

 they have an artist who is not more distinguished for the 

 beauty of his drawings than for his knowledge of the micro- 

 scope, and his intimate acquaintance with the objects to be 

 represented. 



N.B. — Since the preceding pages were printed, I have 

 observed a fragment of Synedra undulans in a slide from 

 Poole Bay, sent to me by the Rev. W. Smith. I have no 

 doubt that the gathering, if searched, will yield entire speci- 

 mens. I am also informed by M. de Brebisson that he has 

 seen the same form in marine gatherings from Brest, but 

 supposed it to be S. gigantea, Lobarzewsky, from which species, 

 however, he now finds it to be quite distinct. 



I may take this opportunity of mentioning that the follow- 

 ing species must be added to the list of known forms in the 

 Glenshira sand, as I have noticed them quite recently. 



233. Gomphonema cristatum. 



234. Mastogloia apiculata. Sm. 



230. Tiyblionella angusta. 



231. „ Scutelhrm. 



232. Amphiprora elegans, Bleakley. 



No. 232 is a splendid marine form, observed last spring 

 by Mr. Bleakley, near Harwich. No. 234 is a very fine 

 marine species, which occurs in great abundance along with 

 232 at Poole Bay. I have understood that Mr. Smith has 

 named it as above, but that it may possibly be referable to 

 another species. — W. G., September 15th, 1854. 



P.S. — Nov. 8th. I have just observed Eunotia Falx in a 

 recent gathering from a point high on the flank of Ben Nevis. 

 This curious species is, therefore, a British one. — W. G. 



