17 



NOTES ON SOME OF THE DISCOID DIATOMS. 



By W. M. Bale, F.R.M.S. 



(Contributed by Prof. A. Bendy, January 2Sth, 1913.) 



In the following notes, written for the most part several years 

 since, I have attempted, in somewhat desultory fashion, a survey 

 of some of the principal characters which have been utilised in 

 the discrimination of species in three or four of the best-known 

 genera of discoid diatoms. Some of the conclusions at which I 

 have arrived as to the inadequacy of many of these distinctions 

 have, I am aware, been reached by previous observers, more 

 especially in the genus Coscinodiscus ; but in such cases the 

 special instances now brought forward may perhaps be service- 

 able in reinforcing those conclusions. In other cases, particularly 

 in the genus Actinoptychus, my observations tend to prove that 

 characters accepted as specific even by recent authors are de- 

 monstrably unreliable. I have not pursued my investigations 

 more fully, as I have found the subject too difficult, owing to the 

 impossibility of procuring much of the literature, and to my total 

 isolation from other observers. I trust, however, that these notes 

 may not be without interest for students of the Diatomaceae, 

 and that the suggestions therein may be of some value to those 

 who occupy themselves with their classification. 



Coscinodiscus. Notwithstanding all that has been done to- 

 wards the elucidation of this unwieldy genus, it still remains the 

 most difficult as it is the most extensive of the whole order. 

 This follows naturally from the general similarity of form, and 

 the absence in most cases of any specialised areas or conspicuous 

 appendages such as serve to distinguish the species in Actin- 

 cptychus, A uliscus, etc. Many forms which have been described as 



Journ. Q. M. C, Series II. No. 72. 2 



