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



EXPLANATION OF ILLUSTRATIONS. 

 Plate VII. 



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

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

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

 missouriensis, 11, Xl^- — 13, Hormotoma latiangularis, X3. — 14, Pterotheca ex- 

 pansa, Emmons. — 15, Cataschisma typa, X3. — 16, Hormotoma jasdata, XH- — 

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

 cott, X2. — 21, Technophorus beUistriatns, X2. 



Issued May 31, 1909. 



