ANIMAL NATURE OF DIATOME^E. 487 



that there is always a coloured substance disposed in 

 lobes, which he supposes to represent the ovaries, in the 

 midst of a transparent and colourless body. 



69. TRICERATIUM. Indwidua libera, lorica bivalvis 

 triangula, in ntroque latere tridentata vel corniculata, non 

 concatenata. 



The perfect resemblance of the primary surfaces, and 

 the large apertures of the three processes in the secondary, 

 render this genus precisely intermediate between Amphi- 

 tetras and Zygoceros\ nor, indeed, can I comprehend 

 how Kiitzing could place them in three separate families, 

 and even in two distinct orders. As to the minute 

 apertures, which Ehrenberg states to be uncertain, in the 

 conjunction of the lateral valves with the median fascia, 

 we may suppose that they are only apparent as in the 

 Biddulphice, where they certainly do not exist. Of the 

 four species hitherto described, two (Favus, striolatum} 

 were observed by Ehrenberg and by Sender in a living 

 state, in the North Sea. 



Like Zygoceros, the Triceratia become detached com- 

 pletely in deduplication, and, therefore, do not, like 

 Amphitetras, form cateniform chains. They possess, also, a 

 more decided motion. This character, however, does not 

 appear to me of so much importance as of itself to fix 

 the limits of distinct families; and Kiitzing himself, 

 who proposes a separate family (Angulatae) for the 

 genus Triceratitim, comprises Zygoceros in that of 

 Biddulphiese, where the catenasform association is so 

 preponderant. 



70. ACTINISCUS. Indwidua solida radiata, stettam 



Although, besides a species exclusively fossil (A. Stella], 

 omitted by Kiitzing, one of the other two has been 

 observed alive by Ehrenberg (A. Pentasterias), and the 

 other exclusively in this state, (A. Sirius,} still we 



