31 



ORDERS 



BELONGING TO THE THIRD CLASS. 



1st Order. Polypi none, or not perceptible. 

 2nd Order. Polypi apparent ; axe inarticulated. 

 3rd Order. Polypi apparent; axe articulated. 

 No Orders belonging to the 4th Class. 



GENERA 



BELONGING TO THE FIRST ORDER OF THE FIRST CLASS. 



Cellepora. Submembranous, in concrete expan- 

 sions. Cells projecting. 



Flustra. Concrete expansions, foliated ; submem- 

 branous. Cells united in formation, and placed in 

 series, on one or many surfaces. 



Pherusa. Flat and frondcscent. Cells oblong, pro- 

 jecting, and only on one surface. 



Electra. Branching. Cells campanulatcd, ciliated, 

 and verticillatcd. 



