NATURAL SCIENCES OP PHILADELPHIA. 213 



Dendrerpeton obtusum Cope. 



This species is known by a partially preserved cranium. The superior sur- 

 face is exposed, the outliues of the jaws and orbits are well preserved, with the 

 occipitt|||condj'les. The os-quadratum is directed obliquely backwards, and 

 the angle of the mandible extends to a line a little behind that of the occipital 

 condyles. The zygomatic arch exists in a position similar to that in which it 

 may be seen in a few genera of Anura, as Discoglossus and Pelobates. It ex- 

 tends downwards and forwards from the suprasquamosal to the maxillary 

 region, but whether it is homologically squamosal or malar, the specimen can- 

 not show. The postorbital is present as well, and with the last, and the su- 

 pratemporal forms the bon}' roof of the temporal fossa. A piece which may 

 be the pre- and postfrontals combined, borders the inner superior margin of 

 the orbit; it widens posteriorly, where it Jias contact with the parietal, etc., 

 and narrows in front. ISupra-occipitals form together a broad triangle on 

 the upper plaue of the cranium, of less extent than the adjoining supratemporal. 

 The latter elements are pitted, and towards their margins radiate grooved. 

 These sculpturings grow less on the margins of the supratemporal, and the 

 portions of the surface of the more auterior element remaining are so slightly 

 marked as to give the impression that the sculpturing in this species is much 

 less than in others of the genus. A few beaded ridges are all that remain on 

 a few of the parietals and postorbitals ; the maxillaries have a slightly 

 stronger sculpture seen in a few spots. 



The general form of skull is elongate behind, and much shortened in front of 

 the orbits. The orbits are thus altogether in front of a line equally dividing 

 the cranium transverselj', while in the D. acadianum Ow. they are in the 

 middle of the skull. The outline of the muzzle in one species is thin, broad, 

 rounded, as in the Menopoma allegheni en sis, while in the latter it is ovate 

 and produced. 



The parietal bones extend to opposite the posterior margins of the orbits, are 

 then gradually contracted and form an acuminate prolongation on each side 

 the wedge-shaped froutals. The prefrontals are thickened on each side the 

 front, behind the external nares. The sutures defining the frontals anteriorly, 

 the nasals, and the premaxillaries behind, cannot be made out. The median 

 longitudinal suture is a marked and zigzag one, and can be seen as far post- 

 eriorly as the anterior margin of the orbits. The external nostrils are large 

 and opposite the inner margin of the orbit on each side. This separation of 

 the nares is associated with a greater transverse extent of the premaxillaries 

 than in some of the genera. These have been set with numerous teeth, judg- 

 ing by their small impressions ; uo larger ones have left traces, and no 

 traces of any on the maxillaries. The teeth of the genera before described 

 are all much larger relatively, indicating still further the diversity between 

 them. 



A fragment of mandible remains, but without teeth or external surface. It 

 shows a large internal canal. 



Measure7ne/Us. 



Lines. 



Total length cranium 25-5 



Width cranium 3 lines behind orbits 24 



'' between orbits 7-5 



" " nares 5- 



" " occipital condyles 2-2 



" of supraoccipital bones 6 



" of right parietal fi 



Extent of premaxillaries 8-7 



Length orbit Ct 



From the Coal Measures at Linton, Columbiana Co., Ohio, (\yest Pennsylva- 

 nia Basin). Discovered by Dr. John S. Newberry. 



Another cranium accompanies the collection which belongs to a species dis- 



1868.] 



