F. B. Loomis — ]\ r e7v Jlosasaur from the Ft. Pierre. 559 



(which is usually in two parts, a smaller anterior and a larger 

 posterior) is so reduced that only the posterior portion remains 

 open. 



The maxillae are heavy bones and each carry but 11 teeth, 

 (a very small number for any mosasaur) which are the typical 

 acrodont, striated, conical teeth, compressed toward the points 

 from the inside toward the outside-. These teeth like those of 

 the lower jaw are rather slender, and from 25 to 30 mm long. 

 All eleven need not be on the jaw at once, for the replacement 

 is of the typical reptilian type in which there is a tendency for 

 each alternate tooth to be in some stage of replacement, in 

 which case even the bony base on which they are situated may 

 be for the time eliminated. 



The prefrontal is short and wide and extends about half way 

 along the external margin of the naral opening, as is typical in 

 Platecarpus. The lachrymal is of small size and bounds the 

 anterior external side of the orbit. 



The frontals are fused into a broad roofing bone, extending 

 from the nares back almost to the parietal opening. There is 

 little distinctive about this bone, except that on either side is 

 a groove beginning shortly behind the naral opening, extending 

 backward obliquely toward the median line, then turning 

 sharply outward and dying out near the orbit about opposite 

 the parietal foramen. 



The parietal is not so bounded that the outline can be made 

 out, but it has a fair-sized parietal foramen. The preservation 

 of the back of the skull does not permit describing the sutures 

 of such bones as the postfrontal, the presquamosal, postorbital, 

 or exoccipital. 



The jugal makes a short arch, which in the specimen found 

 extends laterally; but this is doubtless due to crushing, the 

 normal position of the bones being under the orbit, in which 

 case there is nothing unusual about this bone. 



The quadrate is very characteristic, first in its large size as 

 compared with the rest of the skull. Its lower articular surface 

 for the mandible is rather small, and expanded on the outer 

 side. The body of the bone projects forward and swings in an 

 almost complete circle around the auditory meatus, the supra- 

 stapedial process being very large, its distal end almost reach- 

 ing the base of the quadrate ; but there remains a narrow and 

 well marked opening between the end of the process and the 

 base of the bone, which distinguishes the form from Brachy- 

 saurus where the process is coosified with the base of the 

 quadrate. On the external face of our quadrate the margin of 

 the upper articulation projects laterally, making a rim which 

 extends clear around to the base, in front being developed into 

 a thin plate. The immediate border of the meatus is also 



