96 THE CRAG POLYZOA. 



assert that all the species I have marked as distinct, are really so, or that some of them, 

 at any rate, besides H. frondiculata and retej)oracea, may not be found, upon due 

 comparison, to be identical with other previously described fossil forms. No genus in 

 the whole of this Memoir has required more time or closer examination, and it is only 

 after the most mature consideration that I have arrived at the not very certain conclusions 

 here stated. 



The same difficulty, however, as already observed, would be experienced in the investi- 

 gation even of the living forms, were the inquiry limited to small detached and broken 

 fragments, or to much-worn and injured specimens, such as are, for the most part, offered 

 by the fossil remains. As in several other cyclostomatous genera, more especially among 

 those belonging to the inarticulate section, the aspect of the polyzoary in Hornera differs 

 so extremely in different parts, according to age, &c., that the mere inspection of fragments 

 derived from different portfons of one and the same individual growth, could not fail, 

 from their extreme diversity, to lead to the conclusion that they belonged to distinct 

 species or even genera. It may readily be conceived how much this difficulty is enhanced 

 in the case of fossil specimens. 



The earliest fossil forms clearly belonging to this genus are found, according to 

 Hagenow, in the Cretaceous beds of Riigen and in Sweden, but no species of Hornera 

 as here understood, is noticed by him in the Maastricht beds. Hornera contortilis 

 of Mr. Lonsdale, found in the Cretaceous strata of New Jersey, however, appears to be 

 a well-marked instance of the genus. 



The number of species increases considerably in the Tertiary epoch, and more espe- 

 cially in the more recent strata, in which the genus seems to have attained its maximum 

 development, at any rate in number of forms, if all that are enumerated be really distinct. 



The best marked Tertiary fossil forms, of which we have any published available 

 means of judging, are — 



1. FENESTllATiE, 



1. H. FLABELLiFOliMls, Blainville (sp.) 



Retepora flabelliformis, Blainv. ; Michelin, Icon. Zooph., p. 314, 

 pi. Ixxvi, fig. 1, ^= ? H. Ferussacii, Michelin, 1 Eocene. Miocene. 



2. H. SCOBINOSA, Michel, (sp.) 



Retepora scobinosa, Mich. 1. c, p. 316, pi. vi, fig. 3. Miocene. 



3. H. retepobacea, M. Edwards, Mem. s. les Crisies, &c., p. 21, pi. x, fig. 2. Crag. 



2. Ramose. 



4. H, STRIATA, M. Edivards, 1. c, p. 21, pi. xi, fig. 1. Crag. Michelin, 1. c, p. 317, 



pi. Ixxvi, fig. 7. 



5. H. AFFiNis, M. Edwards, 1. c, p. 19, pl. x, fig. 1 . Upper tertiaries of Sicily. 



