EDWARD D. (OPE. 67 



nearest approximation to the Reptilia is degeneracy, 

 then the changes in this class come under that head. 

 The carpus, tarsus and scapular and pelvic arches of the 

 Rachitomi are more reptilian than are those of any 

 of their successors. 



There are several groups which show especial marks 

 of degeneracy. Such are the reduced maxillary bones 

 and persistent gills of the Proteida ; the absence of the 

 maxillary bones and the presence of gills in the Trachy- 

 stomata ; the loss of a pair of legs and feebleness of the 

 remaining pair in the sirens ; and the extreme reduction 

 of the limbs in Amphinma. Such I must also regard. 

 with Lankester, the persistent branchiae of the Siredons- 

 I may add that in the brain of the Proteid Necturus the 

 hemispheres are relatively larger than in the Anura, 

 which are at the end of the line. 



It must be concluded, then, that in many respects, 

 the Batrachia have undergone degeneracy with the pas- 

 sage of time. 



IV. THE REPTILIAN LINE. 



As in the case of the Batrachia, the easiest way of ob- 

 taining a general view of the history of this class is by 

 throwing their principal structural characters into a 

 tabular form. As in the case of that class I commence 

 with the oldest forms and end with the latest in the or- 

 der of time, which, as usual, corresponds with the order 

 of structure. I except from this the first order, the 

 Ichthyopterygia, which we do not know prior to the 

 Triassic period r 1 



A. Extremities not differentiated in form beyond proximal 

 segment. 



I. Os quadratum immovably articulated to squamosal, etc. 

 Tubercular and capitular rib articulations present and distinct 

 1. Ichthyopterygia. 



lGenerally similar to the system published by me. Proceedings Anier. Ass. Adv. Science, 

 xix, p. 233. See American Naturalist, March, 1885. 



51 



