Qn 
HUDBON-RIVER GROUP; 21 
CORALS OF THE HUDSON-RIVER GROUP. 
Prats 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 Corats flourished in 
that period. And we again find, as before remarked, that as the formation becomes more 
calcareous in its western extension, the Corats 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, favus, honeycomb, and séella, 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 STELLATA (n. sp.). 
Pu. LXXV. Figs. 1 a, b, ec 
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 Favosires, 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 
35* 
