52 Trans. Acad. Sci. of St. Louis. 



EXPLANATION OF ILLUSTRATIONS. 

 Plate VII. 



1, Modiolodon subrhomboideus, X3. — 2-4, Ctenodonta aiiburnensis , X3, 

 an oblique view to show hinge-teeth. — 5-6, Modiolopsis expansa, X3. — 

 7-8, Ctenodonta costata, X3. — 9-l(>, Parallelodus obliquiis. — 11-12, Helicotoma 

 missouriensis , 11, Xl+. — 13, Hormotoma latiangularis , X3. — l-i, Pterotheca ex- 

 pansa, Emmons. — 15, Cataschisma typa, X3. — 16, Hormotoma fasciata, Xl^. — 

 17-19, Pterygometopus lincolnensis, X2. — 20, Pterygometopus intermedins Wal- 

 cott, X2. — 21, Technophorus bellistriatus , X2. 



Issued May 31, 1909. 



