LOWER HELDERBERG ROCKS. 803 



Spirifer modestiis ( n. s.). 



Plate XXVIII. Fig. 1 a - e. 



Shell small, subglobose. Ventral valve very gibbous near the middle and 

 towards the beak, having a shallow undefined sinus extending from 

 the beak to the front : beak prominent, acutely pointed, incurved. 

 Dorsal valve regularly convex, semicircular or subtriangular : extre- 

 mities rounded, sometimes an undefined mesial elevation : beak scarcely 

 extending above the hinge line, not incurved ; hinge line very short, 

 rounded at the cardinal extremities. Area triangular, faintly defined, 

 about half the width of the shell, arcuate. Foraimen of medium size, 

 narrow, triangular. Dental lamellae slightly diverging, and extending 

 more than half way to the base of the shell. 



Surface marked by faint concentric lines of growth. 



This si)ecies resembles somewhat JVucleospira ventricosa of the Lower Helderberg 

 shaly limestone, but has a much higher area : it still more resembles S. lineatus of 

 the Carboniferous system, but differs in its surface markings and its narrower fo- 

 ramen. 



Fig. 1 a. Dorsal view of specimen of ordinary size. 

 Fig. 1 6, c, d. Ventral, dorsal and profile views of a larger individual. 

 Fig. 1 e. The interior of the ventral valve. 

 The margins of the area of this and the preceding species are usually prominent or exsert. 



Geological position and locality. Limestones of the Lower Helderberg group : 

 Cumberland ( Md.). 



Spirifer saffordi ( n. s.). 



Plate XXVIIL Fig. 2 a -/. 



Shell rhomboidal ventricose, a little wider than high : valves nearly 

 equally convex. Hinge line about equalling the width of the shell. 

 Ventral valve much elevated and extended towards the beak, which 

 is slightly curved at the apex : sinus subangular, becoming deep 

 towards the front and much produced. Area twice as wide as high, its 

 width being about half the width of the shell. Ventral valve gibbous in 



