Dixon & Jotry—On Some Minute Organisms. Vol 
The Xanthidia-forms are more definite. We have only 
observed empty cysts. These are spherical chitinous shells from 
which arise a number of short, stout, tubular spines, each appa- 
rently broken irregularly at the apex. The Xanthidia of the 
chalk have been described as the zygospores of Desmids. The 
occurrence of pelagic organisms of this form removes the necessity 
of the unwelcome dilemma, of assuming a partial freshwater 
origin of the chalk (!), or of presupposing marine Desmids.* 
In conclusion of this, which must, at best, be only a prelimi- 
nary sketch, we wish to express our thanks to Dr. E. Perceval 
Wright for calling our attention to a great mass of literature on 
this matter, especially Dr. Wallich’s Papers, dealing with the 
Rhizopoda, and also for giving us the opportunity of consulting 
many of the works needed in his own resourceful library. 
1 Wallich, ‘‘ North Atlantic Sea-Bed,’’ 1862, states that he detected Xanthidia in 
the stomachs of Salpz in the Indian and Mid Atlantic Oceans in 1851. 
[ExpLaNaTIon oF PuatEs. 
