LONSDALE ON EOCENE CORALS FROM N. AMERICA. 



525 



tertiary species found at Hautville 

 and Grignon, and figured as well 

 as described by De France or by 

 Milne Edwards under the names 

 of Idmonea gradata and I. coro- 

 nopus (De F., Atlas Die. Sc. Nat. 

 pi. 46. f. 5. ; Milne Edw., Recher. 

 sur les Polyp., Mem. sur les Crisie, 

 &c. pp. 24. 23. pi. 12. f. 3.) : but it 

 differed in the central blending of 

 the tubular openings ; in this cha- 

 racter there was a certain amount 

 of agreement with the recent spe- 

 cies of Dr. Milne Edwards, I. 

 transversa (sp. cit. pi. 9. and 3.), 

 but in the mode of branching, and form of the branches, marked 

 differences were presented. 



The reverse surface indicated apparently the irregular effects of 

 extraneous agency, and not an uniformity of contour, as in the 

 preceding species. In some fragments the flattening was complete, 

 but the surface was unevenly impressed ; in others, though the 

 triangular form was retained, the reverse side was slightly convex, 

 and in one case partly flat, partly rounded. 



Locality. — Rock's Bridge. 



This figure of Idmonea commiscens, 

 drawn on a greatly enlarged scale, 

 exhibits accurately the central blend- 

 ing of the openings and the great 

 range of the transverse rows, extend- 

 ing nearly to the dorsal surface. 



14. Idmonea. 



Branches divergent, rounded on the reverse side ; rows of tubular openings 

 alternate, projecting, no uniform central blending ; no medial ridge or furrow ; 

 reverse or dorsal side equal half the thickness of the branch. 



The fragments which afforded 

 the above characters were found 

 in the same specimens of friable 

 stone as Idmonea commiscens. They 

 amounted to fifteen in number, and 

 exhibited a great general agreement 

 in the rounding and thickness of the 

 reverse side ; but some variations oc- 

 curred in the distribution of the rows 

 of tubular openings. It was, there- 

 fore, considered advisable to give the 

 above imperfect notice and a figure, 

 without venturing to assign the frag- 

 ments definitely either to I. com- 

 miscens or a distinct species. It re- 

 mains also to be ascertained what 

 amount of differences might be pro- 

 duced in the characters of a species 

 by one portion of a specimen being 

 fixed and another free. 



Locality. — Rock's Bridge. 

 vol. i. n n 



View of Idmonea, of the natural 

 size and greatly magnified. 



