204 ZOOPHYTES. 



The distinction alluded to, of species with short calicles or dupli- 

 cate ridges, and those with the cells separated only by simple ridges, 

 was first made the ground for a subdivision of this genus by Oken, 

 who instituted for the former the genus Favia. Ehrenberg afterwards 

 adopted the same subdivision, but with more accurately defined cha- 

 racters. But the two groups pass by gradual transitions into one 

 another. Moreover, in the Manicinse, the same specimen often 

 shows both the simple and deeply sulcate ridge, according as the 

 coalescence is more or less complete, evincing the little importance of 

 this character as a generic distinction. 



A more important subdivision is suggested by Blainville, who 

 places the species with regular circular cells (a regularity arising from 

 their not increasing by disk buds), in his genus Tubastrcea. Ehren- 

 berg, who first pointed out the source of their peculiarities, separates 

 the same species under the generic name Explanaria, one of La- 

 marck's genera, but much changed in its application. This author, 

 moreover, separates his Explanariae from the Astrrea tribe, and places - 

 them with the Caryophyllacea. While we fail to see the propriety of 

 so wide a separation from the Astraeidae (& 67, 80), there is still some 

 reason for a subdivision of the genus. As the two modes of increase 

 by disk buds and interstitial buds, are sometimes presented by the 

 same species, the groups are introduced only as subgenera. The sub- 

 genus including the Tubastraeae of Blainville, may be called Orbi- 

 cella. The other Astraea simply; or Fissicella, alluding to the mode 

 of growth and budding by subdivision, if a significant name be re- 

 quired. The name Tubastrcea of Blainville, is rejected on account of 

 its formation from words of different languages; as it has not been gene- 

 rally adopted, no inconvenience can result from this course, required 

 as it is by usage and law. 



The Orbicellae have fixed limits to the size of the adult cells, and 

 number of lamella? and tentacles; the cells are circular or ellip- 

 tical, and quite regular. The Fissicellse increase constantly in the 

 breadth of their disks and cells, and the number of lamellae ; the cells 

 therefore are often oblong, and some may be seen in the progress of 

 subdivision ; occasionally they are a little flexuous and lobed, and thus 

 pass into the Meandrinae. The passage also into the Echinoporss, 

 may be distinguished in the erect-lobed species the tesserifera and 

 others allied in which the young appear near the upper margin in 

 the ascending cell. 



Among the Astreeoid corals increasing interstitially, there are some 



