TEKEBRATULID^ 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 appressed 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 Cryptoneixa. This species is shorter, broader 

 and less gibbous than the T. {Cnjiitonella) lincklmni, or the T. (C.) rectirostra ; 

 and it is larger and less gibbous than the T. rooming efin. 



Geological formation and locality. This species occurs in the Corniferous lime- 

 stone, at Clarence-hollow, Erie county, New- York. 



Terebratula sallivanti (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. 



