Lower Helderberg Rocks of Port Jervis, etc. 299 



from this bed, and thus to define more positively the inter- 

 esting problem of its relation to the Coralline of Schoharie, 

 which has usually been claimed as of Niagara age. It 

 plainly overlies the Tentaculite Limestone, in all the quarries 

 of this vicinity. These are now in every case worked in 

 (16), as that furnishes the only lime salable for building 

 purposes; and (2), the Favosite limestone, invariably forms 

 its roof. 



Description of a new species of Pteropod. 

 Genus HYOLITHES, Eich. 



HYOLITHES CENTENNIAUS, N. Sp. 



Shell transversely trigonal or nearly semicircular, tapering 

 gradually and evenly backward for about two-thirds of its 

 length, then more rapidly — becoming conical and terminat- 

 ing posteriorly in an obtuse point. Ventral side slightly 

 convex, narrowly rounded upwards at the lateral edges ; 

 dorsal side convex and narrowly rounded in the highest part. 

 Largest specimen in my possession, one inch and a quarter 

 long, width of aperture four lines, height two and a half 

 lines. The anterior two-thirds taper at the rate of one line 

 in half an inch ; the posterior third tapers more rapidly, and 

 is besides a little elevated. Lines of growth crowded, — 120 

 to the inch, — curved forward very decidedly upon the ven- 

 tral side, and continued straight over the dorsal. The lip, 

 judging from the ventral stria3, must have projected forward 

 rather more than half a circle. 



Geological position and locality ; at the top of the Lower 

 Helderberg group (5c of this paper), near Port Jervis, 

 Orange County, N. Y. 



The specific name refers to the year (1876) in which the 

 description was written. 

 November, 187G. 23 Ann. Lyc, Nat, Hist.j Vol. xi. 



