122 Monogra-ph of the Crustacea of the Cincinnati Group. 



Rather above and in front of the center of each valve, and on its 

 most convex portion, nearly all the species of the genus present a 

 slishtlv raised, circular or suboval swelling:, havine; a diameter of from 

 one fifth to one quarter of the breadth of the valve's surface. This 

 SAvelling is distinguishable by a local change of color or of surface con- 

 dition, and marks the place of a corresponding l*ounded pit, excavated 

 on the interior surface of the valve so deeply as to render the tissue of 

 the valve at the swelling somewhat diaphanous. The cast of this pit on 

 an inner cast of the valve is strongly marked, having a greater relative 

 height than the external swelling. The swelling has usually a reticu- 

 lated appearance, resulting from vascular impressions on the test ; and 

 from a slight sulcus at the margin of the pit a set of delicate canals, 

 tortuous and inosculating, excavated on the interior of the valve, ra- 

 diate forward, downward and backward, gradually becoming fainter 

 toward the edges of the valves. 



Anterior to the central tubercle, or "lucid spot," and nearer to the 

 dorsal margin, is a smaller, but prominent, tubercle on each valve, 

 with a corresponding internal pit. This little tubercle (the anterior 

 tubercle) is usually seated' on or at the edge of a slightly raised area of 

 irregular outline ; and behind it a short, shallow, vertical sulcus, com- 

 mencing at the dorsal margin, is usually apparent. 



LepercUtia Cylindrica — (Hall, 1871.) 



Carapace minute, seldom exceeding yl^^ths of an inch in length, 

 nearly twice as long as wide ; valves very convex and cylindrical, the 

 anterior and posterior ends sub-equal and strongly rounded ; . cardinal 

 line much shorter than the length of the valve ; tubercle obsolete. 

 Surface smooth. Valves do not overlap on the basal border. 



Found within eight feet of low water-mark under the Ohio River 

 bank in Fulton, now part of Cincinnati, at the excavation for Colum- 

 bia avenue, 160 feet above low water-mark, and near the tops of the 

 hills about the city. It is a common fossil, and has an extended range. 



Leperditia viinutissima — (Hall, 1871.) 



Carapace minute, less than rooths of an inch in length, the width 

 being about two thirds of the length, greatest at the anterior third, 

 giving a broadly ovate outline, with a straight cardinal margin, about 

 two thirds of the length of the valves. Surface of the valves smooth, 

 rising into an obtusely pointed prominence at the anterior third of the 

 length; basal margin of the valves not overlapping so far as ascei- 

 taiued. 



