184 DESCRIPTION OF [Polygastrica. 



is smooth, three -sided, with the angles rounded. When 

 two are united, they appear orbicular. Size l-570th. 

 Found amongst conferva. 



163. DESMIDIUM hexaceros. The six-horned Desmidium 

 is represented in plate ii., group 99 ; the figure to the left 

 is a separate one viewed in front, the other an edge view 

 of four. They are generally connected in pairs ; hence it 

 is usual to see six corners or horns. This species never 

 forms a long chain-like body, four (as shewn in the 

 engraving) being the greatest number attached. The 

 body is green ; but the lorica, when empty, is quite colour- 

 less, and then exhibits a distinct central opening. Size 

 l-570th. 



164. DESMIDIUM bifidum. The double-toothed Desmi- 

 dium. The three angles of the lorica of this creature are 

 notched, hence each appears like a double tooth. Size 

 l-570th. Found amongst conferva. 



165. DESMIDIUM aculeatum resembles D. hexaceros; 

 covered with spines. Size 1-5 76th. Found in turf- 

 water. 



166. DESMIDIUM apiculosum. The rough Desmidium 

 has the three angles of its lorica rounded, and is rough. 

 Size 1- 860th. Found in peat-water. 



Genus XLV. STAURASTBUM. The cross-star Animal- 

 cules are characterized by their being free, and pos- 

 sessing a simple univalved four-sided lorica. They are 

 sometimes, perhaps, developed in a filiform chain. No 

 locomotion has been observed ; indeed their only resem- 

 blance to an animal, even as stated by Ehrenberg, is their 

 increase by self- division, though he thinks the green 

 matter within them ova. 



