94 THE CRAG POLYZOA. 



Fam. I. IDMONEID^, Busk. 



Polyzoario erecto, simplici seu ramoso ; ramis cylindricis, vel subcompressis ; liberis, 

 sive inter se conjunctis. 



Polyzoarium erect, simple or branched ; branches cyhndrical or subcompressed ; free 

 or anastomosing. 



1. HoRNERA. Lamx. 



Polyzoario erecto, aut explanato et retiformi, vel ramoso. Cellularum orificiis ad 

 nnam ramorum faciem tantum spectantibus. Superficie anteriori inter orificia plerumque 

 reticulata, fibrosa seu sulcata. 



Polyzoarium ramose ; branches dichotomous and free, or united by short transverse 

 ramules so as to constitute a retiform expansion ; cells opening on one side only of the 

 branches, which surface is marked with wavy anastomosing ridges, in the more or less 

 rhomboidal interstices of which the openings of the cells are situated. 



HoKNEEA, Lamouroux, Exp. Meth., p. 41, 1821; M. Edwards (pars); Reuss (pars); 



Blainville ; Befrance ; Michelin ; Hagenow. 

 Retepora (pars), Lamarck ; Goldfuss ; &c. 

 SiPHODlCTYUM, Lonsdale. 

 MiLLEPORA (pars), Linn.; Ellis and Soland.; Esper.; &c. 



Taking the common Mediterranean Hornera frondicidata, Lamx. (' Expos. Method.,' 

 p. 41, pi. Ixxiv, fig. 7 — 9, or Milne Edwards, ' Mem. s. les Crisies, &c.,' p. 17, pi. ix, fig. 1), as 

 the type of the genus, it may be defined very naturally as above. This definition, however, 

 will exclude from it, besides Idmonea, one or two recent forms, which although agreeing 

 with Idmonea, Hornera, and Frbndipora, in having the openings of the cells on one side 

 only of the branches, yet in other respects approach Pustulipora so much more nearly 

 that they should undoubtedly, if not erected into a distinct genus, be associated with 

 PustuVqmra. But as no instance of a polyzoarium constructed on this type is met with 

 among the Crag fossils, though one appears to have existed in the Cretaceous period {H. 

 tuhulifera, 'Hag. Maast. Kreideb.' p. 2G, pi. ii, fig. 1), it is unnecessary to say more 

 about it in this place, further than to observe that in the forms in question the anterior 

 surface of the branches does not exhibit the peculiar reticulated or fibrous aspect, so 

 characteristic of the true Hornera, though perhaps not entirely limited to them. 



The genus thus constituted appears to be a very natural one ; and it is divisible also 

 into two very natural groups, according as the branches are free or mutually connected by 



