444 DESCRIPTIONS OF NEW SPECIES OF FOSSILS FROM THE 



RHYNCHONELLA MEDIALTS Simpson, n. Pp , Fig. 9. 



Shell broadly oval or subti-igonal in outline ; height a little less than the Avidth ; 

 greatest width about two-thirds the length of the shell from the beak. Margins from 

 the apex to the widest portion of the shell nearly straight, then abruptly rounding 

 and slightly produced in front in a broad extension. 



Ventral valve convex at the sides, depressed in the middle ; mesial sinus com- 

 mencing at the apex and growing wider to the base, where it occupies fully one-half 

 of the width of the valve. 



Dorsal valve unknown. 



Sui'face marked by about twenty i^lications, of which eleven occupy the mesial 

 siiins, niid are smaller than those on other portions of the valve, there being five iu 

 the same sjDace occupied by three of the others ; plications 

 rounded or subangular. There are also very fine radiating striae 

 covering the plications, four or five in the space of 1 mm. The 

 plications are ci'ossed by lines oi* varices of growth. ]S^o con- 

 ^P5 ""^-iAikiiii-^jjg^ centric strije have been observed, though they may occur on more 

 perfectly preserved specimens. 



The specimen from which the above description was taken has a height of 

 25 mm., and a width of 30 mm. 



This species is associated with JRliyncIionella , but may be reodily dis- 

 tinguished by its size and the much laiger number of plications in the mesial fold. 

 The only species approaching it in that respect is li. (S.) venubtula, of the Hamilton 

 group, but they are so unlike in other respects that there will be no difficulty in dis- 

 tinguishino: them. 



Formation and locality. Waverly group, near Warren, Warren county, Penn- 

 sylvania. 



ELIYNCnONELLA STRIATA Simpson, n. sp., Fig. 10. 

 Only the ventral valves of this species have been observed, but they differ so 

 much from known forms that it is necessary to consider them 

 as belonging to a new species. 



Shell subtriangular ovate, apex pointed ; length and width 

 about equal. Margins from the apex to below the middle 

 nearly straight, broadly rounding below, and at the base pro- 

 duced in a broad extension. 

 ^■^■^' Tr.issa Ventral valve convex at the sides, depressed at the middle. 



Mesial sinus beginning near the apex and continuing to the base, becoming very 

 broad as it ajiproaches the front. 



