572 GEOLOGY OF OHIO. 



specifically from the European Orthis calligramma (or perhaps Orihis 

 callaais), then the name Orthis flabeilites, Hall, will do very well to 

 represent the intermediate forms, while the iorms with quite flat brach- 

 ial valves and very convex pedicle valves could be conveniently desig- 

 nated as variety eu-orthis, and the other extreme with more convex brach- 

 ial valves but decidedly flattened pedicle valves would fee variety 

 dinorthis. 



Very closely related to this latter form is a series of shells found at 

 Reed's Hill, in the quarry just north of Beavertown, and at Huffman's 

 Quarry in Ohio. (Plate 37A, Figs. 20 a, b.) The brachial valve is quite;, 

 strongly convex in the specimens from Huffman's Quarry, but very mod- 

 erately convex in most of those from Reed's Hill. The median sinus is 

 chiefly posterior and shallow, w*ith its Outlines undefined. The pedicle 

 valve is very much flattened. In specimens from Huffman's Quarry this 



, flattening is not so marked as to exclude at least a very moderate con- 

 vexity of the shell, especially towards the beak. In valves from Reed's 

 Hill the flattening is more marked, beginning almpst at the very beak, 

 and admitting almost of no curvature anteriorly. The radiating plica- 

 tions are finer and closer and therefore more numerous than in variety 

 ■dinorthis at the same stages of development. The rounded plicatipus 

 are branched, often twice in full grown specimens, a feature shown in a 

 less marked degree by that, variety. A further resemblance to it is the 



' presence of very fine concentric, striae of growth, distinctly visible under 

 a lense. This is the only form of which interiors were found in the Ohio 

 'collection, the previously described interiors having been obtained by 

 cutting away the shell and taking an impression of the cast of the inte- 

 rior thus prepared. The interior of the brachial valve, although 22 mm. 

 long, does not show thickening excepting along a median line, posteriorly, 

 where a rounded elevation, broadening and disappearing anteriorly, serves 

 to separate the muscular area into halves. This muscular area is how- 

 ever not further defined,. the grooves of the exterior showing up as radi- 

 ating plications over the interior of the shell. The cardinal process is a 

 narrow linear and not much elevated ridge. The crural plate is a con- 

 tinuation of the edge of the hinge area bordering the delthyrium, and a 

 well marked, rather deep notch in the outer, angle between it and 

 the hinge area serves as a socket for the teeth. * The interior 

 of a' pedicle valve likewise shows radiating plications, except over 

 the muscular area. This is divided into three parts by two diverg- 

 ing ridges, which are very low, though still distinct enough to be recog- 

 nized. The two lateral divisions are bounded laterally by similar low 

 but more distinct convex ridges, which uniting anteriorly give the area 

 there a circular outline, though the border happens to be very indistinct 

 in front of the middle section in our specimen. The middle division is 

 concave, of about equal size with the lateral divisions, and does not show 

 signs of a median ridge. The interesting feature of this shell is the 



