22 



percentage of infusorial forms, falling on board the " Beagle," 

 when several hundred miles from any land. 



It is considered that those sporious bodies, called Xan- 

 thidium, found in flint are sporangia of Desmids. We have 

 the exact fac-simile of them in the sporangia of the Cosmarium 

 and Staurastrum. Sporangia and empty fronds have been 

 found in tertiary deposits under the bones of extinct mammalia, 

 which fact furnishes us with the strongest evidence of the 

 powers of resistance to change of some of these humble and 

 delicate organisms. 



The uses of Desmidiese are not much known. They evolve 

 oxygen and tend to keep the water clear in which they exist. 

 They also form food for all the entomostraca and many other 

 animalculse. A few months ago I lost a fine gathering of 

 Closterium ascerosum, which I had put aside in a small bottle 

 for the purpose of mounting, by having accidentally admitted 

 a voracious Daphnia pulex ; and I read that a recent observer 

 saw a rotifer, the Notommata myrmeleo, seize a Closterium 

 and suck the whole frond quite free of chlorophyll. 



In giving the subjoined list of Desmidiese I may mention 

 that there are many species which I have not been able to 

 recognise, especially of the genus Closterium. These appar- 

 ently new species I have not ventured to name. At some 

 future time I intend forwarding specimens and drawings to 

 some competent algologist for identification and record. 



For two or three years I have made gatherings of the 

 Docidium verticellatum, figured at page 2. This species has 

 not yet been found in England, although it is abundant both 

 on the Continent of Europe and in America. 



My gatherings have been made mostly from pools which 

 are dug up during the summer. As they are plants whose 

 favorite haunt is the open moor, and are taken in greatest 

 numbers from perennial ponds, I have no doubt but that the 

 Lake District and other likely places would render many rare, 

 and perhaps new forms. 



Most of the species here recorded will be found in the book 

 of drawings. These figures are drawn under the Camera 

 Lucida, and colored most attentively after nature. 



A LIST OF TASMANIAN DESMIDIE^. 



Closterium lunula , Closterium setaceum 

 „ striatolatum „ Ehrenbergii 



„ acerosum „ acutum 



„ rostratum „ 10 species, new 



