8 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 65. 



developed. External nares far in front of the orbits. Nasal bones 

 well developed, embraced by the premaxillae. Periotic bones tightly- 

 wedged among the adjacent bones. Grinding teeth composed of 

 closely adhering columns, usually hypsodont. Enamel very thick. 

 Two pairs of tusksi in lower jaw; none in upper jaw. Genera 

 Desmostylus and Cormcallius. 



EXPLANATION OF PLATES. 



Plate 1. 



Figs. 1-3. Desmostylus. Teeth aud part of skull. XI. 



1. Upper left molar of undetermined species of Desmostylus. Showing 



unworn grinding surface. On the left is a patch of the maxilla, mx. 

 Between the columns of the teeth is seen the cement. Front end 

 upward. 



2. View of same tooth showing the outer face. Front end toward the 



left. Between the columns are seen the tracts of cement. At the 

 hottom of the figure the layer of cement passes between the bases 

 of two fangs of tlie root. 



3. Section across the snout of Desmostylus hesperus. Showing sections 



across maxilloturbinal bones. 



4. Supposed upper molar of CormcalHus sookensi^. Showing grinding 



surface. Type. Front end upward. 



5. Same molar showing the outer face. Front of tooth toward the left. 



Plate 2. 



Figs. 1-5. Teeth of Corn/walUus sookensis (Cornwall). XI. 



1. Supposed left lower molar. Showing grinding surface. Front end 



upwards. 



2. View of .same tooth. Showing outer face. Front end toward left. 



3. View of same tooth, showing a section of fracture across the base of 



the root. Surrounding all is the enamel (e) of the crown. Inside of 

 this is seen the bhickened dentine id). In the center of each fang is 

 seen the matrix filling the pulp cavity (j). c). Front end upward. 



4. View of supposed upper molar. Showing the inner face. Front end 



toward right. 



5. View of same molar. Showing, around all, the base of the enamel e. 



Within this is the blackened layer of dentine, d. Within this is 

 seen the yet large pulp cavity, pc. The front part of this is in a 

 deep shadow. Front end upward. 



