﻿NORWOOD AND PRATTEN ON CHONETES. 27 



Comparisons and Differences. — The depth of the sinus and the height of the ridges 

 alongside of it, will at once distinguish it from all other species. It is true that, 

 while young, it may be mistaken for the G. Flemingii ; but even then its sinus is 

 deeper than in that species, and it has only four spines on the cardinal edge on each 

 side of the beak, while the Flemingii has seven. 



Geological Position and Locality. — This species occurs at Charboniere, Missouri, in 

 the calcareous clays of the coal measures. We dedicate this species to M. de Verneuil. 

 It will at once recall to every one the Productus, which bears his name, as they are 

 both possessed of a remarkably deep sinus. Illinois State Collection. 



Explanation of the Figures. — PI. II., fig. 6, a. View of the dorsal valve. 



Fig. 6, b. Ventral valve and area of the same specimen. 



Fig. 6, c. Longitudinal section of the same. 



C. mesoloba, nob. — PI. II., fig. 7, a, b, c. 



Shell small ; transverse, sub-rectangular. Dorsal valve covered with extremely 

 fine ribs, which, on the margin, number 150. They are everywhere crossed by 

 equally fine concentric striae. This valve is furnished with a very wide median sinus, ' 

 originating near the beak, from which it goes on increasing in width to the front 

 margin. From the bottom of this sinus rises a rounded fold of the same shape as 

 the sinus itself; that is, it is pointed towards the beak, widening from thence to the 

 front, so that its outline is triangular, the base being at the front of the shell. Ears 

 small, and separated from the dorsal vault by a well marked depression, giving to the 

 front of the shell the appearance of being formed of three lobes, separated from one 

 another by the median sinus. Area rather large, and formed from both valves. 

 Deltoid aperture nearly closed by the tooth of the ventral valve. The cardinal edge 

 bears seven oblique spines on each side of the beak. 



Ventral Valve. — Its ribs are like those of the other valve. It has a well defined 

 middle sinus corresponding to the raised fold of the dorsal valve. On each side of 

 this sinus it has a sharp fold opposite to the bottom of the sinus of that valve. 

 Dimensions. — Length, 8 millimetres ; breadth, 11. 



Comparisons and Differences. — At present there is no species of Chonetes known, 

 with which this one can be confounded ; no other one having a medial fold rising from 

 the bottom of the sinus of the dorsal valve. 



Geological Position and Locality. — This species occurs in the limestones and shales 

 of the coal measures ; at Belleville, Illinois; and at Charboniere, Missouri. Illinois 

 State Collection. 



Explanation of the Figures. — PI. II., fig. 8. a. View of the dorsal valve. 

 Fig. 8, b. View of the ventral valve and area. 



