662 S. W. WILLISTON 



of carboniferous times that it must represent a group in itself 

 equivalent to all others then living; and, inasmuch as it could 

 not have left any known descendants, its claim to subclass rank 

 is inoppugnable. 



It has been claimed that the skull of Lysorophus is really mono- 

 condylar, that the condyle is in reality a tripartite one, in which 

 the middle or basioccipital part was represented in life more 

 or less by cartilage, or that the atlas articulated in fact with 

 all three bones- — the basioccipital and exoccipitals. I can not 

 accept this interpretation of the structure. One of the skulls 

 in the Chicago collection has the 'atlas' in close articulation 

 with the condyles, with no interval to correspond to a cartilagi- 

 nous continuation of the middle part. The atlas is transversely 

 truncate in front in the middle, its angles articulating obliquely 

 with the condyles. A second specimen, in which the atlas has 

 been cleanly dislodged, has the condyles quite as they are figured 

 in the cited paper of Case. I will admit that there are some 

 features here which indicate an ossification of the basioccipital 

 and its articulation in the middle with the front end of the atlas ; 

 but, under any interpretation of the structure, the mode of artic- 

 ulation with the atlas is very different from that known in any 

 reptile. While the single condyle in some Cotylosauria may 

 be fiat or concave, in life it was rounded out by cartilage. In 

 no reptile is the condylar articulation known to be concave, 

 as is positively the case in Lysorophus, if it really articulate 

 in the middle with the atlas. 



The general resemblance of Lysorophus to Amphisbaena is 

 conceded, as is also its resemblance to the Gymnophiona, and 

 these resemblances have deceived both Broili and Moodie as 

 to the real relationships of the genus. Both the Amphisbaenia 

 and the Gymnophiona, as also Lysorophus, are or were burrowing 

 creatures, either limbless or with small limbs, with a more or 

 less pointed head, open temporal region, small eyes, and an elon- 

 gated, ofttimes worm-like bod}^ But these resemblances do not 

 necessarily indicate genetic relationships of any of them, any 

 more than do the resemblances between a porpoise and an ichthyo- 

 saur indicate genetic relationships. It is a curious fact that 



