CONTAINING DIATOMACEOUS EXUVIAE. 43 



have, for the convenience of description, grouped them under 

 the name of NavicuJa 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 iindulans 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 Brebesson that he has 

 seen the same form in marine gatherings from Brest, but 

 supposed it to be >S. (/ir/antea, 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. Trybleonella ariiiusta. 



231. „ ScuteUum. 



232. Amphiproraelegans, 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. 



A few Remarks on a Paper, read before the Royal Society by 

 Dr. J. W. Griffith, on the Angular Aperture of Object- 

 Glasses. By Dr. F. d'Alquen. 



In the last number of the ' Microscopical Journal ' an abstract 

 of the above paper was given, and, if you think the subject of 

 sufficient interest to your readers, I should feel obliged if the 

 following observations could appear in your next number, in 

 refutation of the only novel point in Dr. Griffith's paper. 



