Bacillaria.] THE INFUSORIA. 197 



cules contain only one species ; it is characterized by 

 being free, and possessing a simple square compressed 

 lorica, composed of one piece. In its organization it 

 approaches that of Gallionella and Achnanthes. 



208. MICROTHECA octoceros. The eight-horned Micro- 

 theca has a square transparent lorica, with spines, as 

 shewn at Jig. 119 and 120 ; the first being a front, and the 

 latter a side view. It is of a golden colour, variegated ; 

 change of place has not been observed. " I received," says 

 Ehrenberg, " in September, 1832, phosphorescent sea- 

 water from the harbour of Kiel. On the 23rd of October, 

 I found therein this yellow creature, which appeared very 

 similar to a specimen of Anureea, which, together with 

 yellow phosphorescent species of Peridinea, were living in 

 the same water; but no direct evolution of light was 

 observed from M. octoceros." Size l-280th without the 

 spines; with the spines 1-2 10th. 



SECTION II. NAVICULACEA. (Shells siliceous.) 



Genus LV. PYXIDICULA. The round-box Animalcules. 

 These Infusoria possess a simple bivalved siliceous lorica, 

 of a globose form, which is marked by a furrow, where 

 it easily separates into hemispheres. They are never 

 gregarious, or cluster together. They are in organization 

 closely allied to Gallionella. The ova is of a green yel- 

 lowish colour. 



Ehrenberg states, that in August, 1836, he found, in the 

 flints of the neighbourhood of Berlin, numerous spherical 

 bodies, of pretty equal size, the difference in whose 



