LOWER HELDERBERG ROCKS. 
This species belongs to the same group as the preceding; differing from the Nia¬ 
gara S. radiatus in its higher area and rounded cardinal extremities, as well as in 
the depressed rounded folds upon the surface. If, however, we regard the S. cyrtma 
of Dalman as identical with the species from the Niagara and Clinton groups, the 
presence or absence of plications would appear not to be of specific importance. 
In this one, however, this character is combined with so many others, as to render 
the distinction very well marked. 
Fig. 3 a, b, c. Ventral, dorsal, and profile views. 
Fig. 8 d. Enlargement of the surface striae. 
Geological ‘position and locality. In shaly limestone, associated with many species 
common to the Lower Helderberg group : Decatur county, Tennessee. 
Spirifer octocostatus (n. s.). 
Plate XXVIII. Fig. 4 a - e. 
Shell subglobose : valves nearly equally convex. Ventral valve most 
elevated near the beak : sinus angular, extending to the apex : beak 
slightly incurved. Dorsal valve most convex in the middle : mesial 
elevation not prominent : beak rising little above the hinge line, 
slightly incurved; hinge line less than the width of the shell, rounded 
at the extremities. Area triangular, faintly defined, somewhat arcuate. 
Foramen narrow; a strong median septum dividing the muscular area, 
and extending to the apex of the foramen. 
Surface having about four rounded moderately prominent folds on each 
side of the mesial sinus and elevation, which become obsolete towards 
the beaks ; concentrically marked by fine, regular, closely arranged, 
imbricating lamellose strise. 
This species resembles S. crispus of the Niagara group, but is more globose in 
form, has a much shorter area, more rounded extremities, and less strongly marked 
plications. It appears to be intermediate between that species and S. bicostatus of 
the same group, but is readily distinguished from either of them. 
Fig. 4 a, b, c. Ventral, dorsal, and profile views. 
Fig. 4 d. Cardinal view, showing the foramen. Fig. 4 e. Interior of the ventral valve. 
Geological position and locality. Limestones of the Lower Helderberg group : 
Cumberland ( Md.). 
