﻿NORWOOD AND PRATTEN ON PRODUCTI. 13 



P. Wabashensis, nob. — PL I., fig. 6, a, b, c, d. 



Shell small, transverse ; dorsal valve gibbous, enrolled on itself; beak small, pointed, 

 and not passing the cardinal border. This valve is divided in its middle by a wide, 

 deep sinus. The surface is covered by about forty ribs, some of which, however, after 

 leaving the visceral part, unite, so as to form by their junction one thicker rib ; but 

 this character is not constant, as some specimens possess it while others do not. The 

 ears are thin and enrolled ; no tubes have yet been discovered on them. The car- 

 dinal border is of about the same breadth as the greatest transverse diameter of the 

 shell. On the surface of the shell itself there are, generally, from six to eight tubes, 

 very thick and long for the size of the shell, one, still attached, being over seven 

 millimetres long. The transverse folds on the visceral disk are wide and shallow, so 

 as to be hardly apparent. 



The ventral valve is very concave, following nearly the movement of the opposite 

 valve ; ribs like those of the dorsal, but it has neither tubes nor hollows. It is 

 furnished with a very decided varix, corresponding to the sinus of the dorsal valve. 



Dimensions. — Length, 13 millimetres; breadth, 16 mm.; thickness, 6 mm. 



Ribs. — Forty on the entire surface. 



Comparisons and Differences. — When this shell is entirely disengaged from the 

 rock, it cannot be mistaken for any other species; but when the dorsal valve only is 

 exposed, it may be confounded with the P. splendens ; but even then it may be easily 

 recognized by its much shorter cardinal border. If the specimen has lost its shell, the 

 ribs are still shown on the mould in this species, with a series of rounded hollows 

 along each furrow, between the ribs, while in the splendens the hollows are irregularly 

 distributed over the entire surface of the mould, without any appearance of ribs being 

 shown. The nacre of the shell is still very brilliant. 



Geological Position and Locality. — As yet this species has only been found near 

 New Harmony, Indiana, in the middle part of the Coal Measures. 



Explanation of the figures. — PI. I., fig. 6, a. Dorsal aspect of the shell. 



Fig. 6, b. Ventral view of the same, showing the hinge-line and the beak. 



Fig. 6, c. The same, as seen in profile. 



Fig. 6, d. Another specimen, showing one of the long spines. H. Pratten's 

 collection. 



P. elegans, nob. PI. I., fig. 7, a, b, c. 



Shell small; gibbous; longer than broad; dorsal valve curved, and without a sinus; 

 beak inflated, and passing beyond the cardinal border. Cardinal line shorter than the 

 greatest breadth of the shell. Ears small, and covered with a great number of small, 

 slender tubercles. The surface of the shell is covered with rather large rounded ribs, 

 which regularly increase in size from the beak to the front in most specimens, while 



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