Note on the Mandible of Ornithostoma. 



BY S. W. WILLISTON. 



(With Plate I). 

 Almost invariably the skulls of specimens of OniitJiostoma from 

 the Kansas Cretaceous have been found crushed together laterally, 

 obliterating the palatal surface of the maxillae and the buccal sur- 

 face of the mandible. For this reason, the figures hitherto given 

 of the side view of the mandible have been too broad. A specimen 

 recently discovered by Mr. H. T. Martin and now in the Universiy 

 Museum, is fortunately flattened downward and not greatly dis- 

 torted. "T'- In the accompanying plate a partially restored figure is 

 given, showmg the upper view of the specimen. The only points 

 in which the figure may be erroneous are the obliquity of the pos- 

 terior part of the rami and their convexitj^ of outline. From com- 

 parison with other specimens in the museum, it is evident that only 

 a little more than half of the jaws are preserved, the symphysis 

 being fully twice the length of the rami. The specimen is of 

 interest because of its thin, gently concave or flat, horizontal floor 

 of the mouth, which ends in a free, concave and slightly thickened 

 border about one inch in front of the posterior extremity of the 

 symphysis, enclosing below it a long, free cavity, opening back- 

 ward. At each lateral margin there is a free, thin, sharp parapet 

 of bone, about six millimeters in height, standing vertically and 

 having a perfectly smooth border. The floor was probably gently 

 concave, though now flat, In Fig. b is given a cross-section of the 

 jaws at the place marked a, showing the shape of the cavity and 

 the crushing the bone has received. At c is given a restoration of 

 the section at a, showing the outline of jaws very nearly as they 

 must have been during life. It is apparent that the symphysis was 

 rounded and not sharp below. How far the cavity extends for- 

 ward, I cannot say, as the walls are in close contact and pressed 

 flat, towards the distal end of the specimen. The palate seems to 

 have been flat like the floor of the mouth, and it is very evident 

 that if the tongue extended far forward it must have been extremel}'^ 

 thin. 



(01) KAX. UNIV. QU.VR.. VOL. IV. NO. 1. -JULY 1. IHiSu. 



