SYSTEMATIC REVISION 43 



regions are convex. The supraoccipital border Is strongly concave; and the 

 notch separating the epiotic angle from the quadrate angle is as deep as 

 the supraoccipital. The surface of the cranium is thrown into wrinkles with 

 no regular^ pattern and which inosculate to a moderate extent, most so on 

 the preorbital region. The anterior parts of the maxillary and mandibular 

 bones are marked with small, pit-like impressions. 



"Measurements. 



M 



"Total length to quadrate angles measured on the niedian line. . . o. 170 



Length to supraoccipital border 138 



Total width posteriorly 155 



Width at orbits 095 



Width between orbits 021 



Width at nares 062 



Width between nares 030 



Long diameter of orbits 026 



Transverse diameter of occipital cotylus 012" 



See also the description of T. bilobatus. 



Revised description: This is contained in the revised description of the 

 genus. 



Fig. S- — ^Upper view of articular region. X H- 



A. T. insignii. No. 4565 Am. Mus. 



B. T. bilobatus. No. 4562 Am. Mus. 



Table showing distinction of the species T. insignis, T. bilobatus, and T. mesops. 



T. insignis: Posterior angle of the jaw composed of a single tuberosity, an outer 

 tuberosity indicated by a small protuberance. Skull somewhat expanded 

 posteriorly. Orbits in anterior half of skull. 



T. bilobatus: Posterior angle of jaw formed by two subequal tuberosities sepa- 

 rated by a deep groove. Inner side of inner tuberosity vertical with a strong 

 horizontal keel. 



T. mesops: Inner side of inner tuberosity continued inward horizontally, no keel. 

 Skull not expanded posteriorly. Orbits almost exactly in middle of skull. 



Trimerorhachis bilobatus Cope. 

 Proc. Am. Phil. Soc, vol. xx, 1883, p. 629. 



Type: The angle of a mandible. No. 4562 Am. Mus. Nat. Hist. Cope 

 Coll. From Texas. 



Original description: "Among the many specimens of animals of this genus 

 which have passed through my hands, I have not until now been able to 

 select more than one species, the T. insignis. Mr. Cummins, however, now 

 sends me parts of skeletons of four individuals, which present distinctive 

 characters. Two of these include vertebral elements, and all embrace jaws 

 and bones of the limbs and arches. 



"The vertebrae present no important difference from those of T. insignis, 

 but the surface of the intercentrum is not yet cleaned of a thin layer of 

 matrix. The peculiar character of this species is most readily seen in the 

 posterior portions of the mandibular ramus. The angle consists of two sub- 



