52 ; Trans. Acad. Sct. of St. Louis. 
EXPLANATION OF ILLUSTRATIONS. 
Puate VII. 
1, Modiolodon subrhomboideus, X3.—2-4, Ctenodonta auburnensis, <3, 
an oblique view to show hinge-teeth—5-6, Modiolopsis expansa, X3.— 
7-8, Ctenodonta costata, X3.—9-10, Parallelodus obliquus.—11-12, Helicotoma 
missouriensis, 11, X14.—13, Hormotoma latiangularis, *3.—14, Pterotheca ex- 
pansa, Emmons.—15, Cataschisma typa, X3.—16, Hormotoma fasciata, X 14.— 
17-19, Pterygometopus lincolnensis, X2.—20, Pterygometopus intermedius Wal- 
cott, X2.—21, Technophorus bellistriatus, <2. 
Issued May 31, 1909. 
