306 



GEOLOGICAL BIOLOGY. 



FIG. 83. 



FIG. 84. 



FIG. 85. 



FIG. 89. 



FIG. 90. 



FIG. 91. 



FIG. 92. 



FIG. 94. 



FIG. 95. 



FIGS. 83-05. Modifications of the surface features of the Spirifers, expressed in the species of the 

 Niagara period. (After Hall.) 83. Spirifer radiatus Sow. 84, 85. S. plicatella Linn. 

 86. S. eudora Hall. 87. S. Niagarensis Hall. 88. S crispus His. 89. .S. sulcntus His. 

 90. S. bicostatus Hall. 91. .S'. tenuistriatus H. 92. Enlargement of the surface of S. cris- 

 pus. 93. Surface, enlarged, of S. sulcatus. 94. Surface, greatly magnified, of S. Niagaren- 

 sis. QS. Enlareement of surface of S. eudora. 



