FROM THE CRETACEOUS FORMATION OF NEBRASKA. 407 



Explanation of Plates. 



PLATE I. 



FIG. 1, a. Fragment of Callianassa Danai, natural size. 

 " 1, b. The same, enlarged. 



FIG. 2, a. Lingula subspatulata. 

 " 2, I. A portion of the surface, enlarged. 



FIG. 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, I. 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 stria? parallel to the divisional planes. 



FIG. 4, a. Pecten rigida, natural size. 

 " 4, Z>, c. The left and right valves, four times magnified. 



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

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



FIG. 6, a. Lucina subundata, natural size. 

 " 6, b. A portion of the surface, magnified. 



FIG. 7. Cytherea orbiculata, natural size. 



FIG. 8, a. Cytherea tennis^ natural size. 

 " 8, b. Same, four times magnified. 

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



FIG. 9, a- Crassatella Evansi, exterior or left valve. 

 " 9, b. Interior of same. 

 " 9, c. Surface-markings, enlarged. 

 " 9, d. A cast of same species. 

 " 9, e. Profile view of cast. 



FIG. 10, a, b. Nucula subnasuta. 

 " 10, c. Surface-markings, magnified. 



FIG. 11, a. Nucula ventricosa, natural size. 

 " 11, b. The same, greatly magnified. 



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



