AGLAOPHENIA. 285 



The corbula, which is a pinna modified so as to form a 

 protective envelope for the gonothecse, is commonly pre- 

 sent in the former of these groups, but is by no means 

 universal. In one section, of which A. pennatula is the 

 British representative, it is altogether wanting. Where 

 it is present, it occurs under two forms. In A. pluma and 

 allied species it is a closed case; the transverse ribs or 

 girders which constitute the framework are united by a 

 thin chitiiious expansion, and the capsules are thus en- 

 closed in a pod-like receptacle. 



In another section, to which A. myriophyUum and many 

 foreign species belong, the corbula is open ; a number of 

 disconnected curved processes, springing from the base 

 of the hydrothecee, arch over the capsules and afford them 

 a certain amount of shelter. These open corbulae are 

 often of great length, and are very beautiful structures. 

 In the second group of Plumularice the gonothecse are 

 always scattered and unprotected. 



On the whole it seems better to retain the two old names, 

 assigning Lamouroux's to one division and Lamarck's to 

 the other, than to introduce a new term*. 



The genus Aglaophenia is widely distributed, and con- 

 tains many very striking forms. Some of the species 

 attain a very large size. Dana describes the East-Indian 

 A. angulosa as reaching a height of 3 feet, and bearing its 

 plumes, on an average, about half an inch apart, on oppo- 

 site sides ; he computes that the number of polypites on 

 a single specimen is not less than eight millions, " all the 

 offspring of a single germ, and produced by successive 

 buddings." 



* M'Crady and Agassiz have adopted this course. 



