54 Field Columbian Museum — Geology, Vol. II. 



suture beginning just back of the sixth tooth. The distinguishing 

 suture turns upward and backward to meet the anterior end of the 

 external nares in front of the orbit. Above this, for a short distance, 

 the bone is so crushed that the suture is not determinable with cer- 

 tainty, but the upper end is evident, nearly above the middle' of the 

 orbit. The suture separating the two premaxilla? is distinct 

 throughout. 



The maxilla has on each side sockets for twelve or thirteen teeth, 

 all. except a few of the anterior ones, much smaller than those of the 

 premaxilla, and smaller than those of the mandible in this region. 

 From the nares, which are chiefly excavated from this bone, the 

 suture turns upward and backward for about twelve millimeters, sep- 

 arating the nasals ; it then turns downward and backward to join the 

 anterior orbital margin, uniting with the prefrontal. The lower 

 anterior" margin of the orbit is thus formed by the maxillary plate, 

 which shows a shallow groove. The maxillary plate on the left is 

 smooth and undistorted, the nasal and prefrontal having been sepa- 

 rated at their sutures. There is no indication whatever of a separa- 

 tion into two elements, nor is there any free lachrymal. Posteriorly 

 the maxilla forms a rather broad plate below the orbits, having a 

 convex thinned margin continuous with that of the jugal. Back of 

 the middle on this margin, the suture for the jugal turns directly 

 downward for about twelve millimeters, and then backward in a 

 straight line to terminate just beyond the last tooth. 



That element which, in Dolichorhynchops , is described as the 

 supraorbital, is a much more massive bone in Cimoliasaiirus. It 

 unites with the postorbital by a strong suture, behind the middle of 

 the orbit above, and is not separated by a deep notch. as in that 

 specie's. The bone arches forward and downward to beyond the 

 middle of the anterior part of the orbit, as in DolicJiorhynchops, stand- 

 ing out prominently over the orbit and terminates in a strong suture 

 by which it is united to the ascending plate of the maxilla, as has 

 been described. Its union with the prefrontal or frontal cannot be 

 determined in the crushed state of the specimen. Such relations of 

 a supraorbital bone with the postorbital, maxilla, nasal, etc., are almost 

 inconceivable, but are altogether right for a prefrontal. If this be a 

 prefrontal, then the same element in Dolichorhynchops must also be 

 the prefrontal, and the so-called postprefrontonasal is in reality the 

 frontal, while the anterior prolongation from the parietal is in reality 

 a process from that bone, separating the frontals, a most remarkable 

 arrangement for an)- vertebrate skull. I am forced to believe, how- 

 ever, that such is really the explanation of these bones. 



