38 Brachiopoda of the Cinmmati Group. 



occupying a narrow, subcordate depression, which tapers gradually 

 forward to an acute extremity between the anterior ends of the divari- 

 cator scars. Hinge teeth apparently rather small and weak. Vascular 

 markings consisting of two princijml trunks, starting from the anterior 

 lateral angles of the muscular cavity, and each immediately dividing 

 so as to send one main branch obliquely outward and backward, with 

 more or less subdivisions, and another forward with an inward curve, 

 and also giving off more or less subdivisions on the anterior lateral side. 



Surface ornamented by rather coarse, rounded, radiating striae, some 

 of which, on the ventral valve, are entirely simple, and others bifurcate 

 once or twice ; while on the dorsal, they increase in number by th© 

 intercalation of shorter ones between the longer; there being, on a 

 moderate-sized adult shell, about three series of the intercalated ones, 

 the longest of which nearly reach the beak, and soon become as large 

 as the largest, and between these there are a few very short, small 

 ones, near the free margins, and a few others of intermediate length 

 and thickness. A few rather distinct, imbricating marks of growth 

 are usually seen near the free margins of adult specimens ; while under 

 a magnifier, minute concentric lines may be seen crossing the striae 

 and interspaces, and on protected parts of the surface, a strong magni- 

 fier also shows very minute asperities, regularly arranged, and having 

 the appearance of minute, hollow, spine-bases, that sometimes leave 

 minute pits when entirely worn off. 



Breadth of a moderately large specimen, 1.17 inches; length, 0.95 

 inch; convexity, 0.47 inch. 



Found at an elevation of about 500 feet, in the Cincinnati Group, 

 near Oxford, and near Morrow, Ohio. It is a rare species. 



Orthis suhqtiadrata — (Hall, 1847). 



Shell attaining about a medium size, rather distinctly resupinate, 

 somewhat wider than long, subquadrate in outline ; moderately convex ; 

 cardinal margin shorter than the breadth of the valves, and rounding 

 abruptly at the extremities into the lateral mai'gins, which round and 

 converge forward ; front a little sinuous or straightened at the middle. 



Dorsal valve more convex than the other, its most prominent part 

 being near the middle ; mesial sinus small, and rather shallow, some- 

 times continued back nearly to the umbo, or in other instances 

 scarcely more than reaching the middle ; beak very short, or little 

 distinct from the edge of the area, and moi'c or less arched ; area 

 narrow, directed obliquely backward and downward. Interior with 



