1899] A NEW SPECIES OF REVOLVING ALGA 13 



A New Species of Revolving Alga. 



In his studies on the Plankton of the Illinois river (Bull. Illinois Lab. 



Nat. Hist. v. 1898, pp. 273-293, 2 pis.), Br. C. A. Kofoid deals very 



fully with a new species of alga (Pleodorina illinoisensis) belonging to 



the Volvocineae. This form consists of an ellipsoidal coenobium, about 



1 inch in long diameter, containing normally thirty-two bifiagellate 



cells arranged in five rings around the periphery of the hyaline 



gelatinous matrix. In common with most if not all the genera of 



the Volvocineae, e.g. Pandorina, Eudorina, Volvox, one pole of the 



colony is practically always directed forward in locomotion. The cells 



at this anterior end, however, not only differ from those towards the 



posterior pole, in that, as in the genera just mentioned, they are 



provided with larger red pigment spots, but four of them, the so-called 



vegetative cells, are much smaller than the remaining twenty-eight 



gonidial cells. The species, therefore, is especially interesting on 



account of its well-developed structural and physiological polarity. It 



also confirms the opinion expressed by "W. E. Shaw, who founded the 



o-enus, that Pleodorina occupies an intermediate position between 



Eudorina and Volvox, although nearer the former. 



The Corundum of India. 



In these days of the manufacture of artificial rubies it is satisfactory 

 to get reliable information upon the existence and mode of occurrence 

 of the natural stone. 



The well-known "Manual of the Geology of India" being out of print, 

 a new edition of the portion dealing with general geology was. issued 

 in 1893. The portion descriptive of the economic minerals was not 

 at that time re-edited, but is now to be issued in the form of a series 

 of separate papers, each dealing with a single mineral. The first of 

 these is a most elaborate and exhaustive memoir by Mr. T. H. Holland, 

 Deputy Superintendent of the Geological Survey of India, entitled 

 Corundum (Calcutta, 1898, sold at the office of the Geological Survey). 



This paper tell us all that is known about the geological occurrence 

 and geographical distribution of Indian Corundum, and gives much 

 information also about the uses to which it is applied. The most 

 important section is that relating to the geological history of the 

 mineral ; special attention is called to the fact that it is found 

 associated both with basic and with acid rocks. The author is dis- 

 posed to the view that in not a few instances it was an original 

 constituent of the rock, just like spinels and other oxides, and not 

 necessarily an alteration-product or a metamorphic mineral. In 

 particular, a felspar rock in the Coimbatore District, Madras, con- 

 tains unaltered corundum which shows no evidence of secondary 

 origin. It is well known that corundum can be crystallised out from 

 certain slags which contain an excess of alumina. 



