FROM THE CRETACEOUS FORMATION OF NEBRASKA. 407 



Explanation of Plates. 



Plate I. 



G. 1, a. Fragment of Callianassa Danai, xminroX size. 

 ' 1, h. The same, enlarged. 



G. 2, a. Lingula suhspalulala. 



2, h. A portion of the surface, enlarged. 



G. 3, a. Caprinella coraloidea, the external shell partially removed ; showing the interior septate portion, 

 with the thick fibrous shell attached on the inner side of the curve. 



' 3, b. Exterior view of the inner septate portion denuded of the shell, and showing a shallow longi- 

 tudinal groove from the base to near the apex. 



' 3, c. Lateral view of the septate interior portion of the shell. 



' 3, d. Transverse section of the shell at the larger extremity. 



' 3, e. A portion of the fibrous or tubular part of the shell, enlarged, showing solid prismatic columns, 

 which are marked by parallel divisional planes transverse to the longitudinal axis. 



' 3,/. A single column still further enlarged, showing strice parallel to the divisional planes. 



G. 4, a. Pecteti rigida, natural size. 



' 4, b, c. The left and right valves, four times magnified. 



G. 5, a. Avicula Haydeni, natural size. 

 ' 5, b. The same, four times enlarged. 



G. 6, a. Lucina suhindata, natural size. 



' 6, J. A portion of the surface, magnified. 



Fig. 7. Cytherea orhiculata, natural size. 



Fig. 8, a. Cytherea tenuis, natural size. 

 ' 8, b. Same, four times magnified. 

 ' 8, c. A portion of the surface, still further magnified. 



G. 9, a. Crassalella Evansi, exterior or left valve. 



' 9, b. Interior of same. 



' 9, c. Surface-markings, enlarged. 



' 9, rf. A cast of same species. 



' 9, e. Profile view of cast. 



G. 10, a, b. NucuJa subnasuta. 



' 10, c. Surface-markings, magnified. 



G. 11, a. Nuaila ventricosa, natural size. 

 ' 11, J. The same, greatly magnified. 



" 12. Peclunculus Siouxensis, a cast of the left valve. 



