BUDSON'-RIVER GROUP. 275 



CORALS OF THE HUDSON-RIVER GROUP. 



Plate LXXV. 



We have few additional species of the solid corals, beyond those common to the Trenton 

 limestone. The comparatively small amount of calcareous matter furnished during the 

 deposition of the materials of this group, show at once why so few Corals flourished in 

 that period. And we again find, as before remarked, that as the formation becomes more 

 calcareous in its western extension, the Corals increase in number of individuals and 

 species, in some places constituting a large proportion of the rock. In the shaly and 

 arenaceous strata of this group in our own State, we are, for the most part, forced to depend 

 upon the exterior moulds of these forms, the calcareous matter of the coral having been 

 dissolved and removed. In more favorable situations the specimens are well preserved, 

 but they never acquire the perfection and beauty which is seen in those from the same 

 position in Ohio, Indiana and Kentucky. 



Genus FAVISTELLA. 



[Latin, favtu, honeycomb, and stella, a star.] 



Character. Coral massive, hemispheric or globose, composed of polygonal tubes or 

 cells, which increase by interstitial tubes, or by lateral developments of tubes upon the 

 margins of the mass ; cells divided transversely by closely arranged diaphragms, and 

 longitudinally by radiating dissepiments ; extremities of the tubes starform ; rays ( dissepi- 

 ments) about twelve, more or less, meeting in the centre. The rays generally reach one 

 half or two thirds of the distance from the margin to the centre. 



.334. 1. FAVISTELLA STELL ATA (n.*p.). 



Pi. LXXV. Figs. 1 a, i, c. 



Coral hemispheric or spheroidal ; cells polygonal, with diameters of one eighth or one 

 tenth of an inch ; walls of the cells not separable as in Favosites, but apparently composed 

 of a single partition or lamina. 



The tubes are usually six-sided, and two rays or dissepiments proceed from each side ; 

 in other specimens of interstitial tubes there are a less number of sides, and consequently 

 a less number of dissepiments. The diaphragms are usually nearly direct, or bending 

 slightly downward at the margins. 



This species is one of the most beautiful corals among the older rocks. The ends of the 



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