Brachiopoda of the Cincinnati Group. 27 



This bed seems to be 60 or 80 feet thick, back ofMaysville, in 

 Kentucky. Specimens vary in size from that of a pea to that of the 

 largest wabiut. 



OrtMs Icdicosta — (James, 1873), 



This form scarcely attains to more than two thirds the bulk of the 

 larg-est specimens of the 0. lynx, and is always less gibbous, proportion- 

 ally wider on the hinge line, with more angular posterior lateral 

 extremities, and even in the largest individuals it is a much thinner 

 shell. It likewise differs in having its mesial sinus wider and much 

 more profound at the front, and its mesial fold more elevated and an- 

 gular ; while its lateral slopes are decidedly more compressed, those on 

 each side of the sinus being always concave, and the margins of the 

 sinus very prominent and angular, which, together with the prommence 

 of the mesial fold, and the greater length of the hinge line, impart a 

 general angularity of appearance not seen in the lynx. In the sinus 

 there are nearly always three plications, the lateral two being smaller 

 than the middle one, or sometimes rudimentary; while occasionally 

 one of them is obsolete, leaving the large one as usual, in the middle, 

 and a smaller one on one side only. The mesial fold has generally 

 four plications (never more), the middle two being usually larger and 

 more prominent than the others, and separated by a larger and deeper 

 furrow. Its lateral slopes have generally only from five to seven large, 

 simple, angular plications on each side of the fold and sinus ; these 

 being decidedly larger than on specimens of hjnx of corresponding size. 



Internally the ventral valve differs from the hjnx, in having the 

 cavity for the muscular scars much less deeply impressed, owing to the 

 fact that the shell did not thicken within, as in that form, as it ad- 

 vanced in age. Interior of dorsal valve shows the same rudimentary 

 cardinal process ; while its muscular scars are moderately defined, the 

 posterior pair being corrugated and much larger, as well as more 

 widely separated than the anterior. 



Length of a large specimen, 0.86 inch; breadth, 1.40 inches; 

 convexity, 0.88 inch. 



Found"^ on the hills back of Cincinnati, from 300 to 400 feet above 

 low water-mark, and at other localities, but the extent of its range is 

 not known. It is moderately abundant. 



Orthis dentata — (Pander). 



This form is much smaller than the 0. laticosta and always proportion- 

 ally narrower m its transverse diameter. Its hinge line, generally, about 



