SYSTEMATIC REVISION 47 



"The neurapophyses of the vertebra are more elevated and more deli- 

 cate than in the T. insignis, and have the usual median longitudinal groove 

 between them on the median line above. 



"The thoracic shield is represented by a coarsely sculptured plate which 

 is but partially exposed, so that its form is as yet uncertain. 



"The species is smaller than the T. insignis. 



"Measurements. 



MM 



" Length of skull to line of mandibular angles 136 



Width of skull at line of mandibular angles 100 



Length from orbit to end of muzzle (axial) 47 



Interorbital width 25 



Internarial width 29 



Diameter of orbit 12 



Width of mandible at quadrate 25 



Length of four vertebrae over the arches 30 " 



Revised description: See table in revised description of T. insignis, p. 43. 



Trimerorhachis alleni. 



Bull. Am. Mus. Nat. Hist., vol. xxvni, art. xvii, 1910, p. 181. 



Type: Four dorsal vertebrae. No. 4577 Am. Mus. Nat. Hist. Cope Coll. 

 From Texas. 



ii 



Fig. 7. — T alleni No. 4577 Am Mus. X yi. 

 Four dorsal vertebrse, from left side. 



This specimen differs from the type specimen in such important respects 

 that it is necessary to regard it as a new species. The vertebrse are larger 

 than in any of the typical specimens, four intercentra occupying i66 mm. 

 The neural spines show little indication of being divided, but the tops of 

 the spines are still concave and show the former presence of a considerable 

 mass of cartilage. The pleurocentra are proportionately very small. The 

 spines are more erect and there are well-formed posterior zygapophyses. 

 The intercentra are marked on the lower face by deep pits lying on either 

 side of a median keel. The posterior edges of the upper ends of the inter- 

 centra are reflected forward and form a concave facet. 



Genus ZATRACHYS Cope. 

 Proc. Am. Phil. Soc, vol. xvii, 1878, p. 523; Am. Nat., vol. xviii, 1884, p. 36. 



Type: Lost. 



Neotype: An imperfect skull with numerous fragments. No. 4589 Am. 

 Mus. Nat. Hist. Cope Coll. From Texas. 



Original description: "Char. Gen. The existence of this genus is demon- 

 strated by various fragments, the most characteristic of which is a portion 

 of a maxillary bone. This probably belonged to a species of the order Stego- 

 cephali, but whether to the Ganocephalous or Labyrinthodont division is 

 uncertain, though the evidence is in favor of the former. The teeth are in 



