808 Report oF THE STATE GEOLOGIST. 
layer of the shell is usually, probably always, covered with 
numerous fine, short spinules; these, when removed, leave the 
surface with only regularly concentric growth-lines, marked by 
papillz which are the bases of the spinules. 
Type, Spirifera ventricosa, Hall. Lower Helderberg group. 
Distribution. Upper Silurian — Lower Carboniferous. 
Cyclospira, Hall. 1893. 
(Plate 40, figs. 1-3.) 
The type of this genus, Atrypa bisulcata, is a subtrihedral 
shel] with a very convex pedicle-valve and a depressed brachial 
valve. The larger valve has a prominent umbo, the beak being 
closely incurved over the hinge, concealing both foramen and 
deltidium. The umbo is longitudinally keeled, but at about one- 
) 
Fie. 384. Fie. 385. 
The brachidium of Cyclospira bisulcata, Emmons (sp.). 
third the length of the valve a median furrow begins on this 
ridge, widening anteriorly, and thus making a double keel over 
the forward parts of the shell. The lateral slopes are broad 
and smooth, interrupted only in the umbo-lateral regions by 
a short fold on each side, originating at the beak and lying just 
within the margins. 
The brachial valve is slightly convex posteriorly, becoming 
concave medially over the pallial region. The median sinus 
60 
ae a 
a 
ald le sien 
= 
Sa oe a a 
