PLATE XXII. 



The accompanying illustrations are presented to show the principal varieties 

 of structure of the Strophomenoid Brachiopoda. They represent a portion of 

 the work which is being done for the elucidation of shell structure preparatory 

 for the volume of the Palaeontology on the Revision of the Brachiopoda. The 

 specimens are prepared and photographed and the accompanying figures were 

 drawn on stone from photographic prints. 



Fig. 1. Strophomena rhomboidalis, showing the simple rows of large punctae. 



Hudson River group, Ohio. 

 Fig. 2. Strophomena alternata. showing sparse and irregular punctse. 



Hudson River group, Ohio. 

 Fig. 3. Leptaena sericea, showing the oblique tubuli of the shell. 



Hudson River group, Tenn. 

 Fig. 4. Strophodonta magnified. This species shows numerous large punctae 

 and the concentration of the laminae of the shell around the 

 tubuli. OrisJcany Sandstone., Canada West. 



Fig. 5. Strophodonta demissa. The upper part of the figure shows the irregular 

 arrangement of the punctae at some distance below the surface. 

 On the lower portion of the figure, where the section is cut 

 nearer the surface, the punctae are arranged in rows corre- 

 sponding to the radii of the ornamentation of the shell. These 

 features are due to the curvature of the shell which makes the 

 section cut at different depths below the surface. 



Hamilton group, N. Y. 

 Fig. 6. Strophodontarperplana, showing the arrangement of the punctae in nearly 



regular lines. Hamilton group, N. Y. 



Fig. 7. Strophodonta reversa. This figure shows very distinctly the curving 

 and crowding of the fibers and laminae around the tubuli mak- 

 ing them appear like small tubercles. 



Chemung group, Iowa. 

 Fig. 8. Chonetes coronata. The section is cut just below the surface and shows 

 the single row of large punctae coming out along the summits of 

 the costae. The rows of fine crenulations are produced by the 

 laminae forming the sharp concentric striae of the surface. 



Hamilton group, N. Y. 

 Fig. 9. Tropidoleptus carinatus. Section of the shell of the width of two 

 costae, showing the numerous oblique rows of punctae which 

 are more crowded along the summits of the ribs. 



Hamilton group, N. Y. 



All the figures represent an enlargement of twenty diameters. 



