﻿28 NORWOOD AND PRATTEN ON CHONETES. 



Fig. 8, c. View of the dorsal valve divested of its outer coating, and showing the 

 numerous pits distributed over it. 



C. Maclurea, nob. — PI. II., fig. 8, a, b, c. 



Shell somewhat large ; depressed ; transverse, having its greatest breadth near its 

 middle. At five millimetres from the beak the ribs number about thirty ; at one third 

 of the distance from the beak to the margin, most of them bifurcate. Between this 

 and the margin several of them divide again, and when they reach it, they number 

 about one hundred. The furrows between the ribs are of the same size as the ribs 

 themselves. On the internal mould of the dorsal valve, the central furrow is larger 

 than those on the right and left of it, evidently caused by a median tooth, which, 

 commencing at the cardinal edge, traverses more than two-thirds of the length of the 

 shell. On each side of the beak there are eight spines, directed obliquely. The ven- 

 tral valve is slightly concave. Its surface is similar to that of the opposite one. 



Dimensions. — Length, 22 millimetres; breadth, 32. 



Geological Position and Locality. — This species was found at the "Devil's Backbone," 

 Illinois, in limestones of the Devonian period. Illinois State Collection. 



We have great satisfaction in being able to dedicate this beautiful species to the 

 memory of William Maclure, the munificent patron of science, and the father of 

 American geology. 



Explanation of the Figures. — PI. II., fig. 1, a. View of the dorsal valve. 



Fig. 8, b. Same, showing the ventral valve and area. 



Fig. 8, c. Longitudinal section of the same. 



C. variolata, A. a" Orbigny, sp. — De Koninck's " Monograph on the Genus 

 Chonetes." PL XX., fig. 2. 



Geological Position and Locality. — Guernsey, Ohio, in coal schists. 



C. armata, Boucliard. — De Koninck's Monograph. PL XX., fig. 14. 

 Geological Position and Locality. — Devonian, " Devil's Backbone," Illinois. 



C. nana, de Verneuil. — De Verneuil's " Russia and the Ural Mountains." 

 Geological Position and Locality. — Devonian, Falls of the Ohio. 



C. sarcinttlata, Scldotheim sp. — De Koninck's Monograph. PI. XX, fig. 15.' 

 Geological Position and Locality. — Devonian, "Devil's Backbone," Illinois. 



C. Tuomti, nob. — PI. II., fig. 9, a, b, c. 



Shell small ; depressed ; transverse, having its greatest breadth near the middle of 

 the shell. Area excavated mostly at the expense of the dorsal valve. Deltoid aper- 

 ture small, open ; the tooth of the ventral valve fitting into it and partially filling 

 the aperture. The dorsal valve is but slightly convex ; the ventral valve is still more 



