40 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



only ones whose inferior surfaces are exposed. I observe narrow faces for intercen- 

 tra between them. Of the scapular arch the clavicle and a median element are 

 preserved. The former has a narrow subvertical portion which rests on the anterior 

 edge of the scapula, and a horizontal portion which is considerably expanded, con- 

 tracting gradually to the middle line. The median element is T-shaped, with the 

 median portion or stem rather slender. It is broken off posteriorly, so that its apex 

 can not be described. It underruns the expanded clavicles, and may be, therefore, 

 supposed to be a cartilage bone and a true sternum, and not an interclavicle. A 

 superficial layer of the exposed part of this element is roughened by sculpture, and 

 probably represents the interclavicle. The inferior layer of the expanded part of 

 the clavicle is similarly sculptured. The humerus has greatly expanded extremities 

 and a slender shaft of moderate length. The form is similar to that of Pariasaurus. 

 There is an angulation of the distal extremity which represents the condyle. Ent- 

 epicondylar foramen well developed; no ectepicondylar foramen." 



Revised description of the genus (based on all known specimens, as the type is 

 in very poor condition) : 



1. Skull more elevated than Pariotichus; more acuminate. 



2. Orbits large; in the posterior half or the middle of the skull; looking laterally. 



3. Teeth obtusely conical or blunt. 



4. Maxillary teeth increasing in size to the fourth or fifth and then diminishing. 



One or all of the incisor teeth enlarged. 



5. Teeth in more than one row in the maxillaries and mandibles. 



6. Basioccipital and basisphenoid not enlarged. 



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



8. Skull with a definite reticulate sculpture. 



9. Scapula, coracoid, and procoracoid united. 



10. Cleithrum absent. 



11. Ischium and pubis broad and plate-like. 



The following species of Captorhinus are considered as determinable: aguti, 

 angusticeps, isolotnus, and aduncus. No material illustrates better the difficulty of 

 making species in vertebrate paleontology; each specimen might be considered as 

 distinct and numerous species formed with characters given; or, with a little more 

 freedom, all might be placed in a single species. The large number of specimens 

 seem to fall into these four species and to be determinable with a fair degree of 

 certainty. 



Table showing the species of Captorhinus. 



Smaller; median upper incisors larger than the others, they increase in size regular toward 



the median line. The third, fourth, and fifth maxillary teeth larger than the others . . . agutx 



Larger; median upper incisors abruptly larger than the others and bent sharply backward. 

 The fifth maxillary much larger than the others, the succeeding teeth much smaller 

 than the preceding angusticeps 



Larger; resembles angusticeps but the skull proportionntely wider behind. The propor- 

 tions of the parietal bone different tsolomus 



Smaller, size of aguti; median upper incisors abruptly larger than the second pair but not so 

 much so as in angusticeps. Fifth maxillary larger than the first four, the sixth and 

 seventh diminishing in size from the fifth but larger than the succeeding teeth . . . aduncus 



