STEWART: VARIATIONS IN THE GENUS XIPHACTINUS LEIDY. I1lg 
The variation in size is as marked as the other differences 
mentioned above, thus: the length of the maxillary from the pre- 
maxillary varies from 183 mm. to 325 mm., giving a difference of 
142 mm. inthe length of the alveolar borders of the mandibles of 
these two specimens, Nos. 3 and 179; there is a difference in 
length of 98.5 mm. The transverse groove mentioned by Cope* as 
one of the characters of X. molossus, varies greatly in development. 
In some specimens it is very prominent, in others scarcely notice- 
able. The tubercular exostoses on the anterior margin of the 
premaxillary vary quite as much as the other characters enumerated; 
they probably increase in development with the age of the animal. 
However, this, with the presence or absence of a ragged suture 
between the maxillary and premaxillary would not affect the 
specific position of either form under consideration. Other differ- 
ences in outline, etc., are noticeable in the figures and are not 
worthy of mention here. 
In the light of the above facts it would seem that X. molossus 
and X. ¢hawmas are synonymous, and as Cope has admitted that 
X. thaumas and X. audax are synonyms,+ this form should be 
known in the future as A7phactinus audax Leidy. 
*)], c. 19. 
res 
Lawrence; Kas., March ro, 1898. 
