IDMONEID^I. 103 



acquainted with the protean habits of this perplexing genus. But having an abundant 

 supply of well-preserved specimens of the true Mediterranean H. frondiculata, I have 

 been able beyond all doubt to satisfy myself that it is perfectly correct to associate the 

 small palmate forms depicted in figs. 1, 2, PI. XV, with the large and expanded growth 

 usually represented as that of H. frondiculata ; nor can any hesitation, I think, be felt in 

 placing H. ajfinis, M. Edwards, in the same category. With respect to //. andeyavensis, 

 Michelin, the mere comparison of the figure of that species in the ' Iconographie Zoophy- 

 tologique ' with a branch of H. frondiculata will at once show their complete identity, 

 which appears to have been strongly suspected even by M. Michelin himself. Mere 

 differences in the size and disposition of the branches are obviously, in this species, of no 

 importance whatever. The chief specific characters appear to be 



1. The ramification being for the most part in the same plane, or nearly so. 



2. The emargination of the border of the mouth, which thence assumes a bifid 

 aspect. 



3. The coarse perforation of the dorsal surface. 



As before stated, I had formerly confounded with this species one which occurs in the 

 Northern Seas, but which differs in all the above respects very widely from the true or 

 Mediterranean form. The mouth, for instance, in H. borealls is cut off obliquely, so as to 

 exhibit a single acute point, whilst to show the importance of attention even to a single 

 minute character, in H. tridaetylites (nob.} the oral margin is furnished with two, three, or 

 more, acute denticles. All this renders it the more difficult to determine fossil species, 

 in which the apparently important character derivable from the condition of the oral 

 margin is, usually, wholly obliterated. 



10. H. STBIATA, M. Edwards. PI. XV, fig. 3; XVI, fig. 5. 



Polyzoario csespitoso ; ramis cylindricis. Superficie anteriori, reticulato-fibrosa et 

 in areolas rhomboidales divisa; posteriori sulcis, e linea media longitudinal! oblique 

 divergentibus ornata ; sulcis minute punctatis ; costis glabris vel subgranulosis. Cellu- 

 larurn orificiis in seriebus longitudinalibus plus minusve regulariter dispositis, parvis, 

 orbicularibus, ad partem ramorum inferiorem annulo elevato incrassato, subinde uno latere 



acuminato niarginatis. 



Polyzoarium cespitose ; branches cylindrical ; months of cells disposed more or less 

 regularly in longitudinal series, small, orbicular, those towards the lower part of the branches 

 with a raised, slightly thickened, annular border, which is sometimes produced into an 

 acute angle on one side ; a pore above and below the mouth, interior surface marked with 

 smooth reticulated ridges, forming nearly regular diamond-shaped arcolae; posterior sulcate, 



