PRIMITIVE REPTILES 663 



the loss of the lower temporal arcade, and the open condition 

 of the temporal region, as in these forms, the snakes, hzards 

 and salamanders, seems to be correlated with a head resting more 

 or less prone upon the ground. 



In my opinion Lysorophus has no direct ancestral relation- 

 ships with any modern vertebrates; that the Urodeia, or even 

 the Gymnophiona, began in such extremely Amphiuma-like 

 forms in the carboniferous would be contrary to all our paleon- 

 tological experience. The whole structure of Lysorophus dem- 

 onstrates its aquatic habits, in the chiefly perichondral ossifica- 

 tion of its bones; in the widely separated sutures of the skull, 

 as urged by Miss Finney; in the large and doubtless perennially 

 functional branchiae; and in the mode of its occurrence, in beds 

 of immense numbers, coiled up and in undisturbed positions. 



The ribs of Lysorophus are usually described as single-headed, 

 attached to a prominent diapophysis; and this is true for nearly 

 all of them, but apparently not for quite all. In what appear 

 to be anterior ribs, those probably attached near to the head, 

 there is a distinction into head and tubercle, separated by a 

 short neck. Just how the capitular end is articulated has not 

 been determined, though it appears to be attached to a facet 

 immediately below the diapophysis; it almost certainly does not 

 articulate intercentrally, nor has any centrum been found show- 

 ing a parapophysial facet, such as characterizes the contempor- 

 ary Crossotelos. 



The occurrence of limb bones in Lysorophus seems assured. 

 To determine if possible whether the first specimens of limbs 

 found associated with skeletons of Lysorophus were accidental 

 or not, I some time ago requested Miss Marian Finney, a student 

 of paleontology in the University of Chicago, to make a careful 

 search of the abundant material preserved in the collections. 

 I give the results of her studies, which I can corroborate, in her 

 own words, as follows: 



