SYSTEMATIC REVISION 39 



7. Clavicle and interclavicle with external sculpture (?). 



8. Unknown. 



9. Humerus small, without condyles. Articular ends nearly paral- 



lel, without prominent processes. 



10. Femur without ridge on ventral surface. 



11. The two halves of the neural spine still separate. 



12. Intercentrum very thin, leaving large notochordal space. 



Genus TRIMERORHACHIS Cope. 



Proc. Am. Phil. Soc, vol. xvii, 1878, p. 524; Proc. Am. Phil. Soc, vol. xix, 1880, 

 p. 54; Am. Nat., vol. xvin, 1884, p. 32. 



Type: A fragmentary skull with a series of vertebrae. No. 4565. 



Paratype: A skull N0.4557, Am.Mus. Nat. Hist. Cope Coll. From Texas. 



Original description: In the first paper Cope gave the following: 



"Char. Gen. The centrum is represented by three cortical ossifications 

 of the chorda-sheath, a median inferior, and two lateral. The lateral pieces 

 are quite distinct from each other, and are in contact with the neurapophyses 

 above and the posterior border of the median segment in front. The neural 

 arch joins chiefly the lateral elements, but is in slight contact with the 

 lateral summits of the inferior element. The halves of the neural arch are 

 coossified and support well-developed zygapophyses, but no neural spine. 

 A lateral expansion of the base of the neurapophyses represents the diapophy- 

 sis, but it is horizontal and thin. 



"The cranial bones are sculptured with pits and reticulate ridges. The 

 parasphenoid bone is flat. The external nostrils are large and superior, 

 and not anterior. The angle of the mandible is little produced, and the 

 glenoid cavity is transverse and wider at the inner than at the external 

 extremity. The inner wall of the mandible descends from the glenoid fossa, 

 including, with the horizontal outer wall, a deep internal pterygoid fossa. 

 No coronoid bone or process. Symphysis short. 



"The teeth exhibit the inflected dentine of this and allied groups. So 

 far as preserved, they are simply conic, but there are none with the apices 

 complete. There are two series on each side of the upper jaw, both of which 

 consist of larger teeth at their anterior portions. The anterior teeth of the 

 inner row beneath the external nares are much the largest. A thin, bilateral 

 bone from some part of the roof of the mouth supports some large teeth, 

 and a row of small ones diverging from them on each side. The mandibular 

 teeth are in one principal series and become a little larger anteriorly. Near 

 the symphysis there are on each side, within the external row, one or two 

 large teeth. The ribs are short and little curved, and they have flat, expanded 

 heads. They are attached to the diapophysial expansion of the neural arch. 

 Such limb bones as are preserved are without condyles, and are of relatively 

 small size. 



" Trimerorhachis difl'ers from Archegosaiirus in the ossification of the 

 basicranial elements; in the absence of attached neural spines; and in the 

 regular and definite tripartite ossification of the chorda-sheath. The form 

 of the cranium of Trimerorhachis is unknown." 



In the second paper cited Cope added considerably to his previous 

 description: 



"Generic characters, etc.: The type of skull is that of the order of Stego- 

 cephali generally. The superior walls are thin, and are sculptured on the 



