46 PALEONTOLOGY OF KENTUCKY. 



This species resembles closely Orthis michelini, of Laveille, but shows several 

 points of difference. The later species is here, in our Carboniferous rocks, 

 greatly more compressed. 



Formation and Locality. The specimens figured show the general size. Occurs in the upper 

 strata of the Devonian formation in Jefferson county, Ky., and in Clark county, Indiana. 



Genus Tropidoleptus. Han. 



Tropidoleptus, Hall. Pal. N. Y., Vol. IV., p. 4041867. 

 Etymology: tropis, a carina; and leptos, slender. 



Shell transversely sub-oval or semi-elliptical, concavo-convex; hinge-line 

 extended, not crenulate ; articulating by teeth and sockets. Ventral valve 

 convex, with a distinct area and wide fissure beneath the beak. Dental 

 lamellae distinct from the margin of the fissure ; crenulate. 



Dorsal valve concave, with crenulate dental fossets ; a strong cardinal pro- 

 cess with diverging lobes in interior, which support slender crura that converge 

 to and unite with the median crest. Surface plicate ; shell structure punctate. 



Type of the genus is T. carinatus. 



Tropidoleptus carinatus. CONRAD. 



Plate XVII., figures 14 and 15. 



Strophomena carinata, Conrad. Ann. Geol. Rep., p. 64 1839. 

 Leptaena laticosta, Hall, in 1883. 

 Leptaena laticosta, of Owen and others. 



Tropidoleptus carinatus, Hall. Tenth Rep. on St. Cab., p. 151 1857. 

 Tropidoleptus: Genus described and illust. in 12th Rept. on St. Cabinet. 1869. 

 Tropidoleptus carinatus, Hall. Pal. N. Y., Vol. IV., p. 4071867. 



Shell of medium size, concavo-convex, semi-elliptical, length sometimes 

 nearly equalling width ; hinge-line variable in size, but generally a little less 

 than greatest width of shell ; cardinal extremities rarely rounded, generally 

 forming with the lateral margins an obtuse or right-angle. The lateral mar- 

 gins are of double curvature, starting from the cardinal extremities, they curve 

 at first inward for about one- fourth of the length, thence they curve outwards, 

 combining with broad curve of base to an almost regular semi-circle. 



Ventral valve ventricose, sub-carinate in the center by a stronger and more 

 elevated plication, forming a kind of mesial fold, from which the valve slopes 

 in a gentle curve to lateral and basal margins ; umbo small, and the beak 

 somewhat encroached upon by the broad foramen ; cardinal area narrow, ex- 

 tending to the extremities, its margins almost parallel with t}ie hinge-line ; 

 the cardinal angles deflected. The area is longitudinally striate, which feature 

 is, however, obliterated in silicified specimens. 



