EXPLANATIONS OF PLATE IV. 



PAGE 



Fig. 1. a, b, c PLANORBIS VETERNUS. 107 



1 a. Side view natural size. 

 1 6. Same enlarged. 



1 c. Section (enlarged) through the middle, showing the two sides to be nearly equally concave, and 



the greater transverse diameter of the whorls, than in the direction of the plane of the shell. 



Fig. 2. a, 6 VALVATA? SCABEIDA. . .113 



2 a. View of the shell (enlarged) partly imbedded in the matrix. 



2 /). Natural size same. 



Fig. 3. a, b PHOLADOMYA HUMILIS. . 104 



3 a. Side view of an imperfect cast. 

 3 6. Dorsal view of same. 



Fig. 4. a, b. . . . . THRACIA ? SCBLSVIS (casts). . . . 102 



Fig. 5. ... MYACITES NEBRASCENSIS (an imperfect cast). . . . .100 



Fig. 6. a, b, c. . . . . MYACITES SCBELLIPTICUS. ' . . . . .101 



6 a. Side view of a cast. 



6 6. Dorsal view of same. 



6 c. View of the interior, and cardinal margin of another specimen ; hinge plate broken a little behind. 



Fig. 7 ASTARTE FRAGILIS .94 



Fig. 8. . .... THRACIA ARCUATA . 102 



Fig. 9. a, b, c AMMONITES HENRYI. . 123 



9 a. Side view of a cast. 

 9 4. Profile view of same. 



9 c. An enlargement of one of the septa. 



Fig. 10. a, b, c. . . . BELEMNITES DENSUS . 126 



10 a. Specimen consisting of the lower part of the guard broken off near the extremity of the 



alveolar cavity. 

 10 b. The broken end of same. 

 10 c. Part of the lower extremity of another specimen, fractured longitudinally so as to show the 



lateral position of the axial liue. 



