ORIGINAL COMMUNICATIONS. 



On the Marine Diatomace^ of Northumberland, with a 

 Description of Several New Species. By Arthur 

 Scott Donkin, M.D., L.E.C.S. Edin., Lecturer on 

 Medical Jurisprudence in the Newcastle-on-Tyne Col- 

 lege of Medicine, in connection with the University of 

 Durham. 



In my previous communication"^ on this subject, I believe 

 I was the first to point out to observers, that in many locali- 

 ties on the sands of the open shore, marine Diatomacese, in a 

 living state, can be collected in great abundance ; and several 

 to whom I have sent slides, or gatherings, have had oppor- 

 tunities of judging of their richness and purity ; amongst 

 whom I may mention my friends. Dr. Greville, Mr. Roper, 

 and Mr. Okeden. Since the publication of my former con- 

 tribution, the ample experience of three consecutive sum- 

 mers has led me to arrive at the conclusion, that the presence 

 of Diatomaceaj on the sandy beach of still bays is not an 

 accidental occurrence, or the result of peculiarities of season ; 

 but, on the contrary, that such localities are the natural habi- 

 tat of the free species belonging to this highly interesting 

 class of microscopic organisms, and that, in such localities, 

 these species are annually, during the spring and summer 

 months, generated in surprising abundance. But my 

 observations have led me to infer that certain conditions are 

 essential to their propagation on the open shore. These are — 

 1, a clean sandy beach ; 2, a still or calm condition of the 

 water by which this beach is washed ; 3, a certain degree 

 of warmth in the sand. 



On the first of these conditions I may remark, that mud 

 seems to be inimical to the propagation of free marine 

 species ; for in muddy localities, otherwise favorable to their 

 propagation, they are either entirely absent or very thinly 

 scattered over the surface. As to the second condition, they 

 are never found on such portions of the beach as are subject 



* ' Trans. Micr. Soc. London,' vol. vi, p. 34, new series. 

 VOL. I, new ser. a 



