Brachiopoda of the Cincinnati Ch'oup. 49 



the front, and the ventral in the umbonal region ; hinge line equaling 

 the greatest breadth, lateral margins intersecting the hinge nearly at 

 right angles, and rounding to the front, which is regularly rounded, 

 or sometimes faintly sinuous in the middle. 



Dorsal valve flat at the umbo and raised into a rounded, more or 

 less prominent mesial elevation at the front ; beak scarcely distinct 

 from the cardinal margin, which has a very narrow area. Interior 



Fig. 5. — Interior of Dorsal Valve. 



showing cardinal process short and deeply bifid, with very diverging 

 socket ridges on each side, and a small mesial ridge extending forward 

 from its base about one fourth the length of the shell ; sockets for the 

 teeth of the other valve well defined, and rather wide apart ; muscu- 

 lar scars subquadrate and longitudinally furrowed from the socket 

 ridges ; vascular markings well defined and somewhat harp-shaped 

 anterior to the muscular scars ; punctate structure distinct. 



Ventral valve a little convex at the umbo, and impressed or bent so 

 as to form a shallow mesial sinus at the front, that rarely extends back 

 to the middle ; area well defined, rather high, flat, and a little inclined 

 back over the hinge ; foramen closed by a triangular, convex, pseudo- 

 deltidium ; beak not projecting or incurved, but inclined backward 

 with the area and perforated by a minute circular aperture at the apex. 

 Interior with cardinal edge sharp and distinct ; hinge teeth oblique, 

 trigonal, and prominent ; dental laminse extending forward and curv- 

 ing a little, but not meeting at the ends, forming a deep, somewhat 

 half elliptical cavity, marked with an obscure, central ridge, and 

 parallel radiating furrows. 



Surface of both valves ornamented by rather fine, more or less 

 bifurcating, radiating striae, which are crossed by finer strise and dis- 

 tinct marks of growth. 



Length of a large specimen, 0.G3 inch ; breadth, 0.84 inch ; con- 

 vexity, 0.20 inch. 



This form may be readily distinguished from the H. simiata, by 

 both the internal and external characters. Indeed, no two species 

 in the genus seem to be farther apart in their internal markings. 



Figure 5 is a representation of the internal part of the dorsal valve 

 from a .specimen in the collection of Mr. U. P. James. 



