6l6 PHILOSOPHY OF ZOOLOGY. 



by the Millopora (Lam auk), Retipora, &c. and includes 

 the curious family Coral linadic. 



B. Cells originating from a stony base, and forming 

 tubes which are prominent, as Tiibulipora of Lamark. 



C. Tubes parallel, and joined by transverse plates, as 

 Tuhlpora tnimca. 



D. Cells vesicular, and somewhat external, as Cellipora 

 and Eschara. 



E. In the preceding groups, tlie coral is brittle and 

 stony ; in this it is flexible, as Flustra, Cellularia, and Al- 

 cyonium, (represented by A. gelatinosum *.) 



2d Tribe. 



Polypi surrounded by a membranaceous tube, covering 

 all the subdivisions of their compound body, and allowing 

 the head and tentacula to protrude at the simple or cellular 

 sunmiit. This includes, as the types of as many subdivi- 

 sions, the genera Sertularia -f, Tubularia and Alcyonella, 



(Lamark). 



Order III. 



Polypi naked, or destitute of a coralloid covering. In 

 this order there is one genus, which seems to be fixed, with 

 a tough subcoriaceous integiunent, termed Coryna :j:, and 

 probably more complicated in its organization than the 

 other, named Hydra, which is capable of displacing the 

 base by which it adheres. 



• It is probably at the conclusion of this tribe that we should place the 

 fresh-water genera Cristatella (Lam.) and Difflugia, which are free, and the 

 Plumatelia (Bosc.), which is fixed. 



-|- The Sertularia gclatinosa is delineated, Plate v. f. 3. a nat. size, b. 

 mag. The numerous subdivisions of this Linnf.an genus are unfolded by M. 

 l.AMODRoux in his " Histoire dis Polypiers Coralligene.s," Paris, 1816. 



^ Two British species are delineated, Plate v. C. squamata. f. 1. a. nat. 

 size, b. mag. C glandidosa, f. ?. a. nat, size, b. mag. 



