LABI DOS AURUS COPE 315 



The atlas cannot be made out in any of the connected specimens. 

 Doubtless there is also a proatlas. The axis scarcely differs from 

 the following vertebrae. There are twenty-five presacral vertebrae, 

 definitely shown in specimen No. 177. This is the number found 

 by Case in Captorhinus, and one less than the number in Limno- 

 scelis, a genus which has not a few points of resemblance to 

 Labidosaurus. It is two more than is possessed by Seymouria, 

 and three or four more than in Diadectes. In Pantylus the num- 

 ber is unknown. 



The postaxial, presacral vertebrae are scarcely distinguishable 

 from each other, except the five posterior ones, which have no pro- 

 cesses for rib articulation. The spines anteriorly are a little more 

 slender, giving greater freedom of vertical movement. The trans- 

 verse processes anteriorly are a little longer, standing out beyond 

 the margin of the zygapophyses ; they are also a little stouter here, 

 extending down farther on the sides of the centrum. The inter- 

 centra anteriorly are small, not nearly filling out the space between 

 the margins of the centra. There are two sacral vertebrae; the 

 first bears a stout rib, with a broad, vertical face, as long as the 

 centrum, for articulation with the ilium; the second has a much 

 smaller rib, only touching the ilium behind and below the first rib. 

 The caudal vertebrae, so far as known, are narrower than the pre- 

 sacral, and have more slender processes. Their ribs are co-ossified 

 with the centra, unlike those of Seymouria. 



The first and second ribs are slender; the third is broader and 

 much longer. The fourth, as in Captorhinus, is remarkable (Fig. 1) 

 and would hardly be recognized as a rib if found isolated. Its 

 length is less than three times the width of the distal end. It is 

 narrowed in the middle and much expanded at its extremities. 

 Like the early ribs of Seymouria, Diadectes, and Limnoscelis, its 

 function was the support of the scapula. 



Pectoral girdle (Figs. 5, 6). — -In five different specimens, the pec- 

 toral girdle, more or less complete, is found in position with the 

 skull and but slightly dislocated from its association with the 

 vertebral column. In each case the front end of the interclavicle 

 with its articulated clavicles lies between the angles of the jaws 

 and immediately under the occipital condyle — precisely its posi- 



