﻿NORWOOD AND PRATTEN ON CHONETES. 25 



Dimensions. — Length, 15 millimetres; breadth, 22. 



Geological Position and Locality. — This species occurs in the shales of the coal measures, 

 at Belleville, Illinois. 



Explanation of the Figures. — PI. II., fig. 2, a. View of the dorsal valve. 



Fig. 2, b. Ventral aspect and area of the same. 



Fig. 2, c. Longitudinal section of the same individual. 



This species is dedicated to the memory of William Smith, the father of strati- 

 graphical palaeontology. Illinois State Collection. 



C. Fischerl— nob.— PI. II., fig. 3. 



Shell of medium size ; transverse, having its greatest breadth at about one third the 

 distance between the cardinal border and the front margin. Dorsal valve slightly but 

 regularly convex. Ears not separated by a depression from the dorsal vault. It has 

 no ribs, properly so called, but in place of them the surface is covered with an innu- 

 merable quantity of extremely fine strice, which radiate from the beak. These stria? 

 are crossed by concentric ones equally fine, giving it the appearance of fine net work. 

 There are five long thick tubes on each side of the beak, which project in nearly 

 straight lines backwards from the shell. 



Area and ventral valve unknown. 



Dimensions. — Length, 20 millimetres; breadth, 30. 



Geological Position and Locality. — This shell occurs at Burlington, Iowa, in beds 

 which are considered to be at the base of the mountain limestone. It is named in 

 honor of the founder of the genus. Illinois State Collection. 



Explanation of the Figure. — PL II., fig. 3. View of the dorsal valve. 



C. Littoni, nob. — PL II., fig. 4, a, b, c. 



Shell small ; slightly transverse, having its greatest breadth near one third of the 

 distance from the cardinal border to the front margin. Dorsal valve very convex and 

 furnished with remarkably fine ribs, which number about 120 on the margin. Area 

 contracted and hollowed out of both valves ; deltoid aperture very narrow. On the 

 cardinal edge we can see the traces of tubes without being able to count them. Ven- 

 tral valve very concave, leaving but a small space for the lodgment of the animal. 

 Ribs like those of the other valve. 



Dimensions. — Length, 15 millimetres ; breadth, 20. 



Geological Position and Locality. — This species occurs at the Devil's Backbone, 

 Illinois, in Devonian limestone. Dedicated to Prof. A. Litton, of St. Louis, Missouri. 

 Illinois State Collection. 



Explanation of the Figures. — PI. II., fig. 4, a. View of the dorsal valve. 



Fig. 4, b. View of the ventral valve and area. 



Fig. 4, c. Longitudinal section. 



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