MORPHOLOGICAL REVISION OF THE AMPHIBIA. 



Suborder MICROSAURIA. 



Family DIPLOCAULID^ Cope (p. 15).* 



Genus DIPLOCAULUS Cope (p. 15). (Plates 1-5 and 12.) 



Characteristic specimens: Nos. 4470, 4472 Am. Mus. Nat. Hist, and Nos. 

 610, 650, 651, and 652 University of Chicago. 



Setting aside the extremely doubtful Diplocaulus pusillus Broili, the 

 members of this genus are all characterized by the peculiar crescent-shaped 

 head with elongated horns, formed by the tabulare. The genus has been 

 described more or less fully by Cope (45), Broili (4), and Williston (70). 

 The following description is based upon these accounts and upon personal 

 observation of the specimens : 



The skull is triangular or crescentic with a deep, posterior, concave 

 emargination, and the angles of the skull are continued into great horns of 

 solid bone. The nostrils are terminal and the orbits are far forward in the 

 skull; the latter are small and round and look directly upward. The skull 

 is very flat and even depressed in the parietal region. The whole upper sur- 

 face of the skull and the lower jaw is marked by a sculpture of fine pits and 

 reticulate lines; this seems to be the same over all parts of the skull. The 

 mouth is short and very wide, the articular surface for the lower jaw being 

 near the anterior third of the skull. The position of the bones is shown in 

 figs. I and 2, pp. 17 and 18. 



The premaxillaries are small elements forming the termination of the 

 nose and not taking part in the bordei of the nares. They support a single 

 row of teeth. Both Cope and Williston interpreted two small bones on the 

 outer side of premaxillaries and forming the posterior rim of the nares as 

 nasals. This permits the premaxillaries to unite directly with the frontals 

 behind, a rather unusual relatio n. In specimen No. 4470 Am. Mus. Nat. 

 Hist., D. limbatus, there is evidence of a suture across the elements, called 

 by Cope and Williston the premaxillary, dividing it into an anterior portion, 

 the premaxillary, and a posterior portion, the nasal. This would make the 

 bone on the side the lachrymal instead of the nasal, and the relations would 

 appear more normal. The only objection to this interpretation is that the 

 lachrymal {t) is excluded from the orbit by the junction of the prefrontal 

 and frontal. 



The frontals are very lar ge elements imperfectly divided on the median 

 line and reaching from the nasals to a point far behind the orbits. They 

 form the inner rim of the orbit, widely separating the prefrontal from the 

 combined postorbital-postfrontal. 



The parietals are separated on the middle line and inclose near their 

 anterior border a smal 1, parietal foramen. Rather narrow in the fore-and- 

 aft direction, they are extended laterally in correlation with the developing 

 horns. 



* Page references after names refer to the Systematic Revision. 



8S 



