O. C. Marsh— Vertebrate Life in America. 851 
our American extinct forms, so far as we now have them, 
throw little light on their ancestry. This is essentially true, 
also, of our Plesiosauria, Lacertilia and Ophidia, although sug- 
gestive facts are not wanting to indicate possible lines of 
descent. With the Crocodilia, however, the case seems to be 
different, and Huxley has clearly pointed out the path for 
investigation. It is probable that material already exists in 
nuine “missing link,” a saurian (Diplosaurus) with 
