﻿30 NORWOOD AND PRATTEN ON CHONETES. 



Fig. 9, b. — Internal surface of the ventral valve of another specimen of the same 

 age. 



Fig. 9, c. — Curvature of the dorsal valve. 



C. Koninckiana, nob. — PI. II., fig. 11, a, b. 



Shell small ; depressed ; transverse, having its greatest breadth on the cardinal line. 

 Dorsal valve slightly convex ; no sinus ; covered, with the exception of its ears, with 

 fine dichotomous ribs, numbering twenty-two near the beak, and fifty on the margin. 

 The furrows between the ribs are of about the same size as the ribs themselves. Ears 

 flattened ; and without ribs. Area unknown. The cardinal edge has two spines on 

 each side of the beak, placed near the extremities, which project slightly from the 

 edge and then turn downwards, and run nearly parallel with it. The lower ones, 

 which appear like a continuation of the edge, project three-tenths of an inch beyond 

 it. Ventral valve concave, leaving a very small space for the lodgment of the animal. 

 Its ribs are like those of the dorsal valve. 



Dimensions. — Length, 11 millimetres; breadth 17. 



Ribs. — At the margin there are sixteen in the space of five millimetres. 



Comparisons and Differences. — This species can, on account of the length and peculiar 

 direction of its spines, not be confounded with any other. 



Geological Position and Locality. — It occurs in Devonian limestone, two miles west 

 of Jonesboro', Union county, Illinois. Illinois State Collection. 



This very curious species is named in honor of M. de Koninck, whose admirable 

 " Monograph " on the genus is known and appreciated by every geologist. 



Explanation of the Figures. — PI. II., fig. 11, a. View of the dorsal valve, with its 

 spines. 



Fig. 11, b. Curvature of the dorsal valve. 



C. Logani, nob. — PI. II., fig. 12, a, b, c. 



Shell small ; transverse ; having its greatest breadth near the cardinal border. 

 Dorsal valve inflated ; without a sinus ; covered with about thirty rugose ribs. Ears 

 small, and scarcely separated from the dorsal vault. Beak rather large and recurved. 

 Ribs flattened, and crossed by fine lines. Many of them are dichotomous. Area and 

 ventral valve unknown. Traces of tubes can be seen on the cardinal edge, but the 

 number cannot be ascertained. 



Dimensions. — Length, 6 millimetres ; breadth, 9. 



Comparisons and Differences. — This species differs from the C. minida of Goldfuss 

 (sp.,) in the number of its ribs, that species having but twenty-two while ours has 

 thirty. In other respects it resembles it. 



Geological Position and Locality. — This fossil is found at Burlington, Iowa, in the 

 middle portion of the mountain limestone series. Illinois State Collection. 



