150 DESCRIPTION OF [Polygastrica. 



Ehrenberg states that he discovered this species in May, 

 1832 ; and that in August, 1835, he observed the copula- 

 tive process in operation, when some peculiarities were 

 exhibited. On the issuing forth of the green matter, 

 separation took place into four instead of two portions, 

 and the green matter formed itself into a flat eight-cornered 

 body, with a bright spot in its centre, and granulated con- 

 tents. In group 67, the two slender figures on the left 

 side shew their general form, the different positions of the 

 moving points within, and the appearance of the horns. 

 The figure on the right side exhibits the formation of 

 double gemmae, a single creature being by this mode of 

 self-division increased four-fold. Found amongst con- 

 ferva. Length, including horns, l-96th ; without the latter, 

 1 -430th. 



118. CLOSTERIUM rostratum. The beaked Closterium. 

 Lorica slender, spindle-shaped, slightly curved, and much 

 attenuated at both extremities, striated, each horn, beak, or 

 bristle-like extremity, barely as long as the body, often 

 shorter. Length 1-1 20th to 1-4 8th. 



119. CLOSTERIUM? inequale. The unequal Closterium. 

 Lorica spindle-shaped and crescented, striated, and of a 

 tawny colour ; horns unequal, the one blunted, the other 

 long, slender and sharp. Found amongst conferva. Length 

 l-430th. 



