440 



DESCnil'TIONS OF NEW SPECIES OP FOSSILS FKOM THE 



diiced in a conspicuous sublinguiform extension. Sides of the sinus flat, abruptly 

 sloping, making the bottom angular. Area large, triangulai", varying in height ; 

 sometimes nearly equal to the width of the shell, at other times not more than half 

 the width ; slightly oblique ; striated in both dii*ections ; the longitudinal striae dis- 

 tinct ; the vertical striae much fainter and frequently obsolete ; fissure moderately 

 narrow and closed by a convex pseudo-deltidium. 



There are three or four plications on each side of the sinus, the two bounding the 

 sinus being much more prominent than the others. 



Dorsal valve semicircular or subtrigonal in outline; length from one-half to 

 two-thirds the width. Mesial fold broad, prominent, extremely elevated in front, 

 bounded by broader furrows than those between the plications. There are two plica- 

 tions on each side of the mesial fold, the two plications adjacent to the fold being 

 much more i^rominent than the others ; on some of the sj^ecimens nearly as promi- 

 nent as the fold itself, the other two plications being obscure. 



The surface of both valves is ornamented by very fine and delicate concentric 

 striae, which are obsolete on all but the perfectly j^reserved specimens. There are also 

 more conspicuous lines of growth which are most prominent on the anterior portions 

 of the shell. 



This species most closely resembles Cyrtina JiamiUonensis, but may be distin- 

 guished by the two prominent plications adjacent to the medial fold; this feature will 

 serve to distinguish it from other species of the genus at present known. 



Formation and locality. Chemung grouj), three miles north-west of Warren, 

 in Warren county, Pennsylvania. 



SYRINGOTirf RIS ANGULATA Simpson, n. sp., Fig. 5. 



This species closely resembles 8. randalli ; but the specimens are usually of 

 smaller size; the mesial sinus and fold proportionately narrower; the cardinal ex- 

 tremities angular and frequently attenuate. 



J. 



APS, Tr. IS39. 



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

 sylvania. 



