Greenleaf.] 362 [March 10, 



his attention to the cleaning and mounting of these beautiful objects, 

 in preparing a single specimen of Aidacodisciis oreganus, after placing 

 it on the slide, found that it had divided, the upper shell slipping off 

 from the under. This is the most perfect specimen of the division of 

 this class of diatoms I have ever seen, and the most authentic, as the 

 divisions really took place under the eye. 



This is a very interesting object, because it proves, if proof were 

 needed, that these disks are formed of two shells, and thus conclusively, 

 to my mind, revealing the fact that many species have been named 

 by microscopists as new, that are only the thin under layers of the 

 shells of species already classified. I am confident that many of the 

 species named by Dr. Greville, although he was one of the most 

 skilful and diligent of observers, are merely these thin shells removed 

 from their connections. 



In the January number of the " London Quarterly Journal of Mi- 

 croscopical Science," there is a figure given by Dr. Greville exactly 

 like this under shell, which he calls Aulacodlscus orientalis. 



Since writing the above remarks I have seen a letter from Professor 

 Eulenstein to Mr. Charles Stodder, in which he alludes to the paper 

 of Dr. Greville, on Aulacodlscus orientalis^ to which I have referred 

 above . 



Prof Eulenstein, at first thought as I did, that A. orientalis was 

 the inner plate of A. oreganus^ but after a more careful examination 

 of the form, decided it was a new species. He had a slide containing 

 the object. I had only seen the drawing. 



Mr. Stodder is of the same opinion. He says that the granules in 

 A. orientalis differ in form from those of ^. oreganus, being square or 

 oblong, and not arranged exactly in tlie same order. This last vari- 

 ation I noticed in the drawing, but by a careful adjustment of the 

 focus, the variation in this particular is small. Prof Eulenstein says 

 there is a chance of error in examining these disk forms, in mistak- 

 ing an immature frustule, separating from the parent, for the inner 

 plate. 



I should be inclined to hold to my first impression, but must defer 

 to higher authority at present. 



Mr. Greenleaf also stated that he had received from Mr. 

 Samuels several slides of diatoms from a gathering made in 

 Ashley River, S. C, by Dr. Coues, which he had allowed him 

 to report upon. 



