15 



Odontolcce. — The third Subclass, OdontolccB (toothed birds with 

 teeth in grooves), are from the same geological formation and from 

 the same region of country as the last, and were made known by 



Fig. 5. Skeleton of Hesperoinis. 



the same distinguished naturalist, between the years 1870 and 

 1880. The birds forming this subclass were short-winged diving 

 birds, with rudimentary wings and a sternum without a keel. So 

 many complete skeletons of these birds have been found that 



