262 NEW YORK STATE MUSEUM 



Paraptyx Ontario sp. nov. 



Plate 7, fig. 1-8 



Shell of medium size, beak subcentral or slightly posterior, closely 

 appressed against the hinge line, umbones prominent, directed posteriorly, 

 giving the umbonal region a somewhat oblique slope. Outline elongate 

 subovate to subcircular. Hinge line or crescent margin straight or 

 slightly incurved behind the beak, extending to the farthest posterior 

 margin, and making a right or acute angle with that margin ; ante- 

 riorly short, and soon passing into the rounded lateral curve of the 

 valves. Lateral and ventral curves broadly subcircular. Contour 

 normally rotund, specially in the umbonal region, sloping regularly to the 

 lateral and basal margins. The vertical, concave crescentic area is broad 

 crested at its summit, and crossed by obliquely radiating riblets which 

 begin directly under the beak. The first of these radiate in all directions 

 from that point posteriorly, inward and anteriorly, and strongly crenulate 

 the margin. This is specially true of the shortest and least oblique of these 

 radii. The more oblique radii cover the greater portion of the surface. 

 The crest or crescent ridge is greatly elevated, its surface being modified 

 by undulations resulting from concentric lines, which elsewhere are 

 obscurely seen. This structure may be compared with that of the crested 

 anterior limb in Honeoyea, where the strong varices are developed at the 

 crossing of concentric lines not elsewhere visible on the shell. The surface 

 bears from 120 to 150 fine, flat plications, which increase by the intercala- 

 tion of smaller ones and are separated by linear grooves. These .all have 

 a strong posterior curve over the median convexity of the shell. This 

 surficial ornament is altogether similar to that in Cardiola clarkei 

 Beush. with which the shells also agree in all other respects save the 

 presence of the cresent and the more oval outline. Low concentric corru- 

 gations are sometimes seen ; these being in some degree due to compres- 

 sion in the shales. In several of the sculpture casts there are evidences 

 of two or three short, impressed lines diverging from the beak. These 

 would seem in such cases to represent internal umbonal ridges, but they 



