TEREBRATULIDiE OF UPPER HELDERBERG LIMESTONE. 387 
fifths as great as the length, and the depth nearly equal to half the 
length. 
Ventral valve a little less convex than the dorsal; the beak moderately 
incurved and broadly truncated by the foramen : no visible sinus or 
elevation in the middle, of the valve. 
Dorsal valve broadly elliptical or subcircular, somewhat regularly con¬ 
vex ; the beak closely aggressed below that of the opposite valve. 
Surface marked by concentric lines of growth; the shell-structure dis¬ 
tinctly punctate. 
The length of an ordinary specimen is seven-tenths of an inch, the 
width six-tenths of an inch. 
I have continued this species under the Genus Terebratula, without having 
any satisfactory evidence of its internal structure ; though it may hereafter prove 
to belong to the Genus or Subgenus Cryptonella. This species is shorter, broader 
and less gibbous than the T. (Cryjptonella) lindclceni, or the T. (O'.) rectirostra ; 
and it is larger and less gibbous than the T. rcemingeri. 
Geological formation and locality. This species occurs in the Corniferous lime¬ 
stone, at Clarence-hollow, Erie county, New-York. 
Terebratula sullivanti (n.s.). 
PLATE LX. 
Shell elongate-ovate or subspatulate, truncate or emarginate in front, 
of moderate convexity; width and length about as four to six, or 
seven to nine. 
Ventral valve a little less convex than the opposite; the beak much 
extended, neatly attenuate and perforate at the apex; the cardinal 
slopes rounded and a little concave near the hinge margin, usually 
depressed towards the front, and sometimes a shallow sinus which 
reaches one-third or one-half the length of the valve. 
Dorsal valve a little more convex and considerably shorter than the 
ventral valve, usually flattened and sometimes depressed along the 
centre of the lower part of the valve. 
