NIAGARA LIMESTONE OF CHICAGO, ILLINOIS. 85 



might be permitted to infer, from analogy, that the original axis was solid, and resembled 

 the cylindrical stems of other species of the genus, but has been destroyed in our 

 specimens. 



Diameter of the hollow axis, .16 below, .19 above ; diameter of verticils, more than three 

 inches ; number of cells in one tenth of an inch, 6 to 8. 



Much remains to be learned of this coral ; and we desire to direct attention to it by 

 making known, in the mean time, its very extraordinary ensemble. The two species of 

 Cladopora described by us not only present unique characters in their general forms, but, 

 in their structure, furnish us with the proofs that Cladopora is a generic type founded in 

 nature. 



Cladopora fibrosa Hall. Pal. N. Y., II. 139, pi. xxxviii. figs. 4, 5. 



Cladopora seriata Hall. Pal. N. Y., II. 137, pi. xxxviii. fig. 1. 



Cladopora reticulata Hall. Pal. N. Y., H. 141, pi. xxxix. fig. 3. We have specimens of 

 this exhibiting the reticulations spread over a surface eight or ten inches square. 



Halysites catenularia Linn. sp. Seldom found in a recognizable state of preservation. We 

 occasionally find casts of the spaces enclosed by the labyrinthine walls, which, with the 

 vertical striations and transverse wrinkles of the tubes preserved, present an object closely 

 resembling the enigmatical fossil named Cophinus diibius in the Silurian System, (pi. xxvi. fig. 

 12,) and which in the Siluria (p. 136, and pi. xv. fig. 4) is attributed to the slow gyration of 

 the stems of encrinites after the mud had settled around them. The Ludlow fossil may clear- 

 ly have had the origin attributed to it; but our specimens, though at first obscure, have 

 furnished, at length, conclusive evidence of being the impressions or casts of the walls of a 

 Halt/sites. The transverse dissepiments in some of the cells are well preserved and numerous. 



Siromatopora sp ? We have a weathered specimen, exposing the stellately diverging 

 ramulets formed in the interlaminar spaces. This curious organism would not ordinarily 

 be identified as a Stromatopora ; but, by the aid of Dr. Rominger's extensive suite of specimens 

 of this genus, its true character becomes apparent. There is a specimen of the type, which 

 shows stellate cell-mouths, in the Illinois State Cabinet. This is in the usual state of pres- 

 ervation, and may be identical with ours, though we have only had the opportunity to give 

 it a hasty glance. 



Stictoporapunctipora? Hall. Pal. N. Y., II. 157, pi. xl. B, fig. 2 a-c. 



Polypora incepta ? Hall. Pal. N. Y.,II. 167, pl.xl. D,fig. 5 -/. A large undulately cyathi- 

 form frond, nearly six inches in diameter, with fenestrules somewhat smaller than in the 

 typical species. The cells have not been certainly distinguished either in this or the fol- 

 lowing species. 



Fenestella elegans? Hall. Pal. N. Y., II. 164, pi. xl. D, fig. 1 a-g. 



Lwhenalia concentrica Hall. Pal. N. Y., II. 171, pi. xl. E, fig. 5, a-g. 



ISCHADITES Murchison. 



Ischadites tessellatus W. and M. 



Plate II. figure 3. 



Body somewhat tapering, pyriform, compressed on the side toward which the smaller end 

 is slightly inflected ; the larger end imperfect in all our specimens. One example is some- 

 what in the form of a triangular prism with rounded edges, and the sides indented toward 



