PLATE IX 



PAGE. 



Pig. 1-4 . Venustodus Leidvi, St. J. and AV 350 



1 a. View of concave face of tooth : 1 b, convex face ; 1 c, view from above, enlarged two 



diameters : 1 rf, enlargement showing the disposition of the coronal folds in con- 

 cave face; 1 e, enlargement showing folds in convex face; 1/, outline view in profile, 

 enlarged : 1 $, profile section, enlarged. St. Louis limestone ; Alton, Illinois. 



2 a. Outline nat. size, and enlargement showing the concave face of a minute tooth inter- 



mediate in form. Same horizon and locality. 



3 a. Concave face of small arched tooth, enlarged two diameters: 3/>, showing the convex 



face ; 3 c, outline view in profile. Same horizon and locality' 



4 a. View of concave face of still smaller tooth, enlarged two diameters ; 4 b, convex face ; 



4 c. outline of crown from above ; 4 d, outline view in profile; 4 e, profile section. 

 Same horizon and locality. 



Pig. 5, 6. Venustodus argutus, St. J. and W 352 



5 a. Concave face of medium-sized tooth: 5 b, convex" face; 5 c, view of convex face, 



enlarged two diameters ; 5 d, outline from above, showing arrangement of basal 

 folds, eh'arged ; 5 e, enlargement showing portion concave coronal belt ; 5/, similar 

 enlargement of convex face ; 5 g, outline view in profile, enlarged ; 5 h, profile sec- 

 tion. Chester limestone, upper fish-bed ; Chester, Illinois. 



6 a. Concave face of smaller, arched tooth ; 6 6, view from above ; 6 c, similar view, enlarged 



two diameters; 6 d, similar view of one extremity still further enlarged, showing 

 disposition of coronal folds; 6 e, profue section enlarged. Same horizon and local- 

 ity - 

 Pig. 7-14. Venustodus variabilis, St. J", and "W 346 



7 a. Tooth of normal size and form, seen from above; 7 b, profile section. Upper Burling- 



ton limestone ; Louisa county, Iowa. 



8 o. Concave crown face of similar medium-sized tooth ; 8 6, convex face, base restored in 



outline; 8 c, profile section. Same horizon and locality. 



9 a, b. Similar views of a less denticulate variety. Same horizon and locality. 



10 a. View of convex face of large tooth, with laterally compresssed median cone; 10 b, 



profile view. Same horizon and locality. 



11 a- A small, linear, low-crested tootn, seen from above, enlarged two diameters; 11 6, pro- 



file section. Same horizon and locality. 



12 a. View from above of a very flat variety, in which the crest is but slightly raised above 



basal imbrications. Same horizon and locality. 



13 a. Concave face of small, triangular, acuminate tooth; 13 b, convex face; 13 c, profile 



section. Same horizon and locality. 



14 a. Concave face of more robust tooth of same variety ; 14 b, convex face, showing rela- 



tively deep base and interrupted coronal folds; 14 c, profile section. Same horizon 

 and locality. 

 Pig. 15-18. Venustodus robustus, St. J. and "W 345 



15 a. Medium size tooth seen from above ; 15 b, profile section. Upper Burlington; Louisa 



county, Iowa. 



16 a. Convex face of large, sharp-cre.sted form ; 16 b, profile view. Same horizon and local- 



ity. 



17 a. Small linear variety, view from above showing apex but slightly elevated above crest ; 



17 b. profile section. Same horizon and locality. 



18 a. A very small linear form, seen from above, crest forms a low, even ridge, coronal folds 



frequently interrupted, enlarged two diameters; 18 6, profile section. Same hori- 

 zon and localitv. 



