46 A REVISION or THE COTYLOSAURIA OF NORTH AMERICA 



Revised desert ption: 



1. At least twice the size of Captorhinus. Skull acuminate anteriorly, very 



wide posteriorly. 



2. Orbits of moderate size, located near middle of the skull. 



3. Teeth obtusely conical. 



4. Maxillary teeth not greatly different in size. Median incisors much larger 



than others and bent sharply backward. 



5. Teeth in more than one row on maxillary and mandible (Jide Williston).* 



6. Basioccipital and basisphenoid not large. 



7. Supraoccipital plates vertical at the back of the skull. 



8. Skull with reticulate sculpture. 



9. Scapula, coracoid, and procoracoid united. 



10. Cleithrum absent. 



11. Ischium and pubis broad and plate-like. 



Labidosaurus hamatus Cope. 



Pariotichus hamatus Cope, Proc. Am. Phil. Soc., vol. xxxiv, 1896, p. 445, 448. 

 Labidosaurus hamatus Cope, Proc. Am. Phil. Soc, vol. xxxv, 1896, p. 136. 

 Pariotichus incisivus Case, Zool. Bull., vol. 11, 1899, p. 231. 

 Labidosaurus incisivus Williston, Joum. Geol. vol. xvi, 1908, p. 359. 



Type: Same as that of the genus. 



Original description: "Besides exceeding in size the other species, this one is 

 characterized by the elongation and compression of the muzzle, and by the extent 

 of the projection of the premaxillary region beyond and below the mandibular rami. 



"The length of the skull a little exceeds its posterior width. The lateral out- 

 lines expand rapidly from the anterior borders of the orbits, posteriorly, while 

 from this point anteriorly the lateral outlines of the muzzle converge very gradually. 

 The transverse section of the muzzle is subrectangular, and not a segment of a 

 circle as in other species, the superior face being nearly flat and the maxillary borders 

 somewhat contracted. This form may, however, be due to pressure. Opposite 

 the posterior border of the nostril the premaxillary bone is steeply decurved, 

 forming a concavity which receives the extremity of the mandible. The deflected 

 portion of the premaxillary forms a lobe which projects as far as the continuation 

 of the line of the inferior border of the ramus mandibuli. An open emargination 

 of the border separates it from the corresponding lobe of the opposite side. This 

 may be due to accident. The mandible is narrower than the muzzle at the sym- 

 physis; it is a little wider than the cranium at the front of the orbit, but it is narrower 

 than the cranium posterior to it. 



"The orbit has an oval outline, with the long axis anteroposterior, which enters 

 the length of the cranium posterior to it twice, and one-and-three-quarters times the 

 length anterior to it, and a little exceeds the interorbital width. The latter is flat. 

 The posterior outline of the skull forms a wide open emargination. The surface 

 of the skull and jaws is so much injured in both specimens as to render it impossible 

 to state the character of the sculpture, if any existed. 



"The teeth are not well preserved, although where preserved their length can 

 be determined in the limestone matrix. The elongate maxillary tooth is placed 

 exactly half-way between the borders of the orbit and the nostril, which is posterior 

 to its position in the P. aguti. The other maxillary teeth are small in comparison 



* In t paper published iince the preparation of thii manutcript Branton, Journal of Geolofgr, toI. zii. No. a, pp. 135-139, 

 icporta the pretence of more than one row of teeth in the jaw of Labidtsuurus; obterTed in two ipecimeni. 



