34 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



an idea of the character of the lower surface, and the similarity of the axis to 

 Diadectes renders it very probable that the atlas was of the form shown. Ten 

 vertebrae have been added to the extremity of the tail ; this may be wrong by one 

 or two either way, but scarcely more. Williston thinks the tail to have been rather 

 longer than does Case. That chevrons were present is shown by the base of one, 

 and the form of these bones varies so little, in a general way, that it is safe to con- 

 clude that they were nearly as represented ; they may have been a little longer and 

 may have had a slightly different inclination. The phalangeal formula was very 

 certainly the usual one, 2, 3, 4, 5, 3-4; this is shown by the presence of digits on one 

 or another foot carrying 2,3,4, and 5 phalanges. We have assumed that the posi- 

 tion of the tarsus, as it lay in the ground, was correct and little if any disturbed; 

 it seems very satisfactory as compared with other forms. The presence of two 

 centrale in the tarsus is not certain and is improbable. For all other points there 

 is full evidence from the skeleton. 



That Diasparactus was a member of the family Diadectidae there can be no 

 doubt. The general form of the body is strikingly similar and the individual 



Fig. 22. Restoration of Diasparactus zenos. About ,'s natural size. 



bones show differences that can not be reckoned greater than generic. The skull 

 is closer to that of Animasaiirus than Diadectes, but possesses characters of both. 

 The development of the three broad ribs in the cervical region is another close 

 resemblance to Diadectes, which we doubt not will be found in Animasanrus when 

 the skeleton of that genus is discovered. The absence of the plates over the sixth, 

 seventh, and eighth ribs may be natural or may be due to accident. The presence 

 of a well-developed rib on the axis is a new but not unexpected feature. The shoulder 

 and pelvic girdles and the Hmbs are strikingly similar to those of Diadectes; the 

 most apparent differences are in the vertebrae. The high and more slender neural 

 spines are distinctly indicative of habits somewhat different from those of Dia- 

 dectes; if the idea be retained that the Diadectidae were in process of developing 

 a dorsal armor similar to that of Pareiasaurus, which was perhaps realized to some 

 extent in Diadectes, then Diasparactus may be regarded as representing an early 

 stage in the process. 



The animal had gone far toward attaining the strongly articulated vertebral 

 column forming the axis of what must have been a very stiff" and rigid body, so 

 evident in the members of the family, but had perhaps not yet abandoned freedom 

 of motion in the dorsal series so extensively as had Diadectes: this is perhaps borne 

 out by the less powerful sacrum ; in Diadectes the two vertebrae support the pelvis. 



