EXPLANATION OF PLATE XVII. 



Figs. 1-7. ECHINOCONCHUS ALTERNATUS (Norwood and Pratten) p. 138 



1-4. Pedicle, brachial, lateral and posterior views of a nearly com- 

 plete shell without the surface spines. (W. M., No. 14318.) 



Keokuk limestone, Warsaw, Illinois. 



5. View of the interior of a nearly complete brachial valve. 

 (W. M., No. 14316.) 



Crawfordsville shale, Crawfordsvillc, Indiana. 

 6-7. Lateral and pedicle views of a pedicle valve from which the 

 spines are missing. (W. M., No. 14319.) 

 Keokuk limestone, Warsaw, Illinois. 



Figs. 8-9. ECHINOCONCHUS sp. 



Lateral and pedicle views of a large and nearly complete pedicle 

 valve lacking the spines. (W. M., No. 12988.) 

 St. Louis limestone, Carondelet, Missouri. 



Figs. 10-15. ECHINOCONCHUS BISERIATUS (Hall) p. 141 



10-13. Pedicle, brachial, lateral and posterior views of a nearly 

 perfect specimen, lacking the spines. (W. M., No. 14315.) 



Salem limestone, Spergen Hill, Indiana. 



14. The impression of the external surface of a brachial valve. 

 15. View of the interior of a brachial valve. (W. M., 

 No. 14766.) 



Salem limestone, Hull's Hollow, near Alton, Illinois. 



40 



