NO. 1860. A NEW FOSSIL ALLIGATOR FROM MONTANA— GILMORE. 299 



and undistorted. The upper surface of the preorbital region is flat 

 and wdthout crests or ridges; the muzzle is evenly but broadly 

 rounded; the nasal aperture is large and pear-shaped in outline. In 

 the absence of a roof-like covering formed by the premaxillaries 

 over the anterior part of the external nares, Brachychampsa differs 

 from all known alligators, both recent and extinct. On account of 

 the damaged condition of the anterior extremities of the nasal bones 

 it can not be determined whether they extended foward into the 

 narial opening. The facial processes of the premaxillaries extend 

 posteriorly to the level of the aveolus for the fifth maxillary tooth. 

 The nasal bones are comparatively slender and extend posteriorly 

 to the level of the anterior borders of the orbits. In recent alligators 

 these bones terminate well in front of the orbital line. The maxil- 

 laries are broad, flattened above, and much compressed vertically. 

 The jugals are heavy, with roughly sculptured surfaces. The inter- 

 orbital surface is flat and not concave as in many crocodiles and 

 alligators. The orbital openings are everted as in the alligators 

 and some crocodiles and are confluent with the lateral vacuities. The 

 sculpturing of the facial surface of the bones is more strongly marked 

 in the neighborhood of the orbits than it is anteriorly. 



In the palatal view (PI. 27), where the bones have not sufl'ered 

 mutilation, all of the sutures are plainly indicated. Latero-infe- 

 riorly the maxillo - premaxillary suture passes obliquely backward 

 and inward on the palate. The damaged condition of the palate 

 just back of the anterior palatine vacuity renders uncertain the 

 posterior extent of the premaxillaries. In the recent alligators 

 this suture extends nearly straight across on a level with the second 

 maxillary tooth, while in this form it extends posteriorly at least 

 as far as the level of the fourth maxillary tooth. 



Each of the broad maxillaries has alveoli for 14 teeth, and 

 each of the premaxillaries for 5. The palatmes, of which only 

 the anterior portions are present, unite with the maxillae by an almost 

 straight transverse suture on a level with the eleventh maxillary 

 tooth. The lateral borders of the anterior ends of the palatines are 

 divergent, as in all alligators, instead of parallel or convergent as in 

 all true crocodiles. On the left side of the palate enough of the 

 boundary of the posterior palatine vacuity remains to indicate that 

 it was subround instead of elongate as in most members of this group. 

 The preserved borders of the anterior palatine vacuity show it to 

 have been of large size and probably pear-shaped in outline. 



The pits on the palatal surface of the premaxillary for the recep- 

 tion of the anterior teeth of the lower jaw are broad and exceedingly 

 shallow. 



A detached fragment of the pterygoid shows the processes to have 

 been blunt and stout. 



