SYSTEMATIC REVISION 43 



Captorhinus isolomus Cope. 



Pariotichus isolomus Cope, Proc. Am. Phil. Soc, vol. xxxiv, 1896, pp. 445, 446. 

 Pariotichus (?) isolomus Cope, Broili, Paleontographica, Band Li, 1904, p. 86. 

 Pariotichus laticeps Williston, Joum. Geology, vol. xvil. No. 3, August 1909, p. 241. 



Type: Complete skull. No. 4338 Am. Mus. Nat. Hist. Cope Coll. From Texas. 



Original description: "This species is most nearly allied to the P. aguti. The 

 form of the skull is different and also the sculpture. The skull is equilateral, and 

 the posterior superior border is nearly straight. The muzzle projects beyond the 

 mouth border, so that the incisor teeth are directed backwards at an angle of 45°. 

 The nares are separated by a space equal to their long diameter. The orbit is of 

 moderate size. Its anterposterior diameter enters the lengths of the skull anterior 

 and posterior to it 1.75 times, being midway of the total length. It exceeds by a 

 little the interorbital width. The mandibular ramus is robust, being a little deeper 

 than wide, and the angle is small and pinched, projecting behind the articulation 

 and in line with the rising inferior border. The parietal foramen is well developed. 



"In the sculpture of the superior surface of the skull the longitudinal striae are 

 more prominent than the transverse ones which connect them, except on the muzzle, 

 where they are about equally conspicuous. The sculpture is finer and reticulate 

 on the jugal and quadrato-jugal regions. About a dozen longitudinal ridges be- 

 tween the orbits. Sculpture of the mandible tubercular reticulate. 



"Three teeth on each premaxillary bone, of graded lengths, the anterior being 

 much the larger. Posterior to these one or even two smaller teeth may stand on the 

 premaxillary. The large tooth of the maxillary is the third from the premaxillary 

 suture. At the fifth tooth the second longitudinal row appears, and at the eighth 

 tooth, the third. There are ten teeth in line with the row which is external anteri- 

 orly, but posteriorly a short row appears external to this one, which includes five 

 teeth. The crowns of the teeth of the two internal rows are low and compressed, so 

 as to have a longitudinal edge. In the lower jaw there are three rows with com- 

 pressed crowns besides the external row. Posteriorly the marginal and the third 

 row (from without) disappear, and the second and fourth approximate and end in a 

 single tooth in line with the second row. 



"In one of the specimens the cranial roof posterior to the orbit can be lifted off. 

 Above the sphenoid region, viewed from above, there are four subround tuberosities, 

 which look like the casts of cavities. On the inferior side of the roof in the corre- 

 sponding positions are four flat tuberosities, of somewhat different form from the 

 inferior ones, and an obtuse median prominence, which fits into the space between 

 the four inferior tuberosities. These superior tuberosities resemble the casts of 

 cavities left by the dissolution of rwo hemispheres, and two transversely expanded 

 larger, mesencephalic lobes, with a hypophysis between them. This interpretation 

 is, however, very uncertain, especially as the structure does not resemble the cast of 

 the cranial cavity, which I have previously described in Empedias. 



"Measurements. M 



"Length of the cranium on the middle line 0.076 



Width of the cranium posteriorly 063 



Anteroposterior diameter of the orbit 016 



Interorbital width 013 



Width between nares at front of muzzle 009 



Diameter of largest maxillary tooth 0025 



Length of long premaxillary tooth 007 



Diameters of mandibular ramus at fourth tooth: 



Vertical 0105 



Transverse 009" 



4 



