68 PALAEONTOLOGY OF KENTUCKY. 



ating striae, which increase partly by intercalation but mostly by bifurcation 

 on the ventral valve, while it is the reverse on the dorsal valve, where very 

 few of the striae dichostomize, but a great many short ones are implanted. 

 The specimen before me, the only one so far known, measures seven and one- 

 half lines in width, live and one-half lines in length, and two lines in depth. 

 It differs from the other shallow Chonetes by its greater size, and from the 

 larger species by its shallowness. 



Formation and Locality. Found in the 'rotton hornstone in upper strata of the Devonian forma- 

 tion, at the Palls of the Ohio, on the Indiana shore of river. 



Chonetes yandelliana. HALL. 



Plate XVII., figures 16, 17, 18 and 19, and Plate XXXI., figures 20 and 30. 

 Chonetes yandelliana, Hall. Tenth Rep. on State Cabinet, p. 118 1857. 

 Compare : Chonetes lineata, ut sup., page 121. 

 Chonetes yandelliana, Hall. Pal. N. Y., Vol. IV., page 1231867. 



Shell very small, semi-oval, more or less gibbous ; hinge-line equalling the 

 greatest width of the shell ; cardinal extremities angular, but sometimes 

 rounded. 



Ventral valve regularly convex, having its greatest convexity below the 

 umbo of the valve, from where it slopes in a regular curve to the lateral and 

 basal margins, but more abruptly to the cardinal angles, which are slightly 

 deflected, forming there a faint incurvation or concavity ; beak small and little 

 curved. 



Dorsal valve corresponding in its concavity with the convexity of the ven- 

 tral, but owing to the internal cavity of the shell being somewhat less than 

 the ventral convexity. Cardinal area of the ventral valve parallel with the 

 longitudinal axis of the shell, nearly twice as wide in the middle than at its 

 extremities ; foramen comparatively large, with margins projecting and the 

 opening filled by the cardinal process of the opposite valve. Dorsal area 

 extremely narrow, being barely a denned line. Surface marked by fine, almost 

 equal striae, which increase by bifurcation and intercalation till there are from 

 sixty to seventy on the margin of the shell. The ventral valve has on its car- 

 dinal margin three to four short, oblique spines on each side of the center. 

 The interior of the ventral valve shows strong, dental lamellae, and the muscu- 

 lar impressions are pretty well defined. The dorsal muscular impression, are 

 also well marked, and between them there is a strong mesial ridge, which is 

 extended in a bidentate cardinal process. The lower half of the surface is 

 strongly papillose. This species bears a close resemblance to C. lineata, but 

 it is less gibbous, and not flattened on the middle of the ventral valve ; while 

 the interior presents more strongly defined markings. Generally three spines 



