J 16 THE CRAG POLYZOA. 



2. D. GRIGNONENSIS (?), M. Edw. {sp.) PI. XX, fig. 4. 



Sessilis vel adnato. Cellulis elongatis sparsis ; orificio emarginato. 

 Polyzoariura sessile or adnate ; cells elongate, scattered ; mouth notched. 



TcBTJLiPORA GKiGNONENSis, M. Edwards, Mem. sur les Crisies, p. 13, pi. xiii, fig. 2. 

 Habitat.— Q. Crag, 8. Wood. 



Genus 10. Defrancia, Bronn. 



Polyzoario disciformi, solitario seu social!, convexo vel concavo, stipitato vel 

 sessili. Cellulis in costis elevatis e centro radiantibus et ad peripheriani disci latiori- 

 bus, dispositis. 



Polyzoarium discoid, solitary or associated, convex or concave, pedunculate or sessile ; 

 cells disposed in distinct elevated ridges, radiating from the centre and increasing in 

 width towards the periphery. 



Defeancia, Bronn. (? 1825); Ha g enow ; B'Orbigny ; Reuss (pars); Busk. 



TUBULIPORA (pars), M. Edwards; Michelin (sp.) 



LicHENOPORA, IfOrhigny (pars) ; Michelin (non Defrance). 



BiCAVEA, Unicavea, D'Orbigmj. 



Ceriopora (pars), Goldfuss ; {Hagenow in Geintz. Grund.) ; Auct. 



Pelagia, Lamouroux ; Michelin. 



Stellipora (?), Hag. 



Habitat. — C. Crag, 8. Wood; Grignon, Milne-Edioards ; Michelin. 



The species belonging to this genus are numerous, and appear to have existed from 

 a very ancient period, some, according to Hagenow, being found in the oolitic, more in the 

 cretaceous, and fewer again in the tertiary formations, whilst several exist in the living state. 



The polyzoarium may be either solitary, or a number may grow together in 

 such close contiguity as to become fused, as it were, into a common mass, usually of a 

 more or less globose form, though sometimes expanded and encrusting ; these may be 

 termed the associated. 



In the solitary species, again, the discoid or expanded portion may be either 

 sessile and immediately adnate, ox pedunculate ; and any of these divisions may be 

 furthermore split up into lesser groups, according as the surface between the elevated 

 costge upon which alone the cells open, is smooth and entire, or porous. The importance 

 of the latter character was first pointed out by Dr. Hagenow (' Maast. Kreideb,,' p. 42), 

 and was employed by me in an ' Account of the Polyzoa collected on the Coast of 



