﻿24 • NORWOOD AND PRATTEN ON CHONETES. 



our country, four of which are common to the United States and Europe ; and fifteen, 

 as at present known, peculiar to this continent. We must say, however, that there is 

 still another species, brought from the Humboldt river, in Utah, the markings of which 

 are too much obliterated to admit of its being described. It belongs to the Mountain 

 limestone, and is, from its form, evidently distinct from any other one of our species. 

 It was found by Mr. Pratten. 



Genus Chonetes, Fischer. 



C. Shumardiana, de Konihck. — De Koninck's " Monograph on the Genus Chonetes." 

 PI. XX., fig. 1. 



Geological Position and Locality. — In the mountain limestone at Button-mould Knob, 

 Jefferson county, Kentucky. 



C. Granulifera, D. D. Owen. — " Geological Eeport of Wisconsin, Iowa and Min- 

 nesota." Tab. V., fig. 12. 



Geological Position and Locality. — In the coal measures at Belleville, Illinois ; and 

 at Keg Creek, Missouri. 



C. Smithii, nob. — PL II., fig. 2, a, b, c. 



Shell of medium size ; transverse, having its greatest breadth on the cardinal border, 

 which is produced into points. Dorsal valve covered with numerous fine ribs, amounting 

 to about 160 on the margin. It is crossed by broad imbricated folds, marking the 

 successive periods of growth, and showing that its form was the same in all stages. 

 The entire surface is covered with small pits or hollows, as if from the falling off of 

 tubes or spines ; these pits are tolerably regularly disposed in quincunx ; they are 

 always on the summit of the ribs, and are larger and altogether different in shape 

 from the hollows at the bottom of the furrows between the ribs ; these latter being 

 merely fine lines as if drawn by the most delicate graver. It has a wide shallow sinus, 

 which originates at the beak, and goes on increasing in breadth to the front. The 

 area is very large and formed by both valves ; the portion belonging to the dorsal valve 

 being hollowed, while that of the ventral valve is flattened. The deltoid aperture is 

 wide but nearly filled by the tooth of the ventral valve. Ears distinctly separated 

 from the dorsal vault by a wide depression. The cardinal edge has ten tubes on each 

 side of the beak. The ornaments of the ventral valve are like those of the opposite 

 one. On the internal surface of the ventral valve there is a bifid median tooth resting 

 in a socket, and supported by five ridges projecting into the shell, the two largest of 

 which are nearly parallel to the cardinal border ; at a small distance from it, the cen- 

 tral ridge projects about two fifths across the valve ; on each side of this are two others 

 supporting a series of points. All the interior surface, but particularly towards the 

 front, is covered with small points. 



