H. L. Moodie — Ancestors of the ReptUia. 219 



interest to know the condition of the pterygoids in these forms. 

 In the absence of these important structures we must base our 

 conclusions on the structures present. 



In both groups, then, we find the following structures identical : — 

 Ribs intercentral, intercentra absent, vertebrce amphicoelous with 

 notochord persistent, pectoral and pelvic elements identical, number 

 of dorsal vertebrte agrees in some forms, limb bones with well- 

 developed endochondrium which becomes more pronounced in the 

 reptiles, phalanges clawed, hand and foot broad, neural spines of 

 the vertebra? low, rudimentary, or absent. 



The absence of intercentra in the Microsauria is assured. There 

 is not the slightest evidence that the vertebral column is composed 

 of other than the pleurocentra and neurocentra. The intercentra 

 probably developed late in the history of the Amphibia as in the 

 Temnospondylia, and were transrnitted by some of the Amphibia to 

 the reptiles. I cannot believe that the intercentra are inherited 

 from the piscian ancestors. 



The only tangible differences, then, on which to base a separation 

 of the reptiles from the Microsauria is on' the reduced parasphenoid, 

 osseous carpus and tarsus, and two sacral vertebrae. These characters 

 serve well as class distinctions, and we must await further knowledge 

 to unite the earliest forms which we now call reptiles and the latest 

 forms of the so-called Amphibia. It has been suggested that the 

 Microsauria do not furnisli forms which could have given rise to 

 the broad-headed Cotylosauria and their allies. But members of 

 the new genus Erpctosaiirus bear very close resemblance to these 

 forms. The skull is closely sculptured, broad, and heavy. The 

 members of tliis group and its allies might well have stood in an 

 ancestral position to the later forms. 



The Microsauria as known, however, are confined to the land and 

 marsh dwellers, and we know nothing as yet of the inhabitants of 

 the open seas, if there were any. It is quite possible that some 

 members of the group such as (Eatocephalus, which was a good 

 swimmer, took to the sea, and from some form like this was developed 

 the Ichthyosaurs, Mesosaurs, and the other aquatic forms. One 

 thing which tends to militate against the Microsauria is their small 

 size ; if, however, it is taken into account that not all the Microsauria 

 were small but that it is only the small ones which are well known, 

 this objection can have little weight. "We shall undoubtedly some 

 day know the other forms of which we have now only faint traces, 

 and although we may not then call them Microsauria tliey may 

 nevertheless serve to bridge the gap between the Amphibia and 

 the Reptilia. The occurrence of Isodectes, so similar in form and 

 structure to the Microsauria, in the same bed with them leads one 

 to think that they were already an old race ; and the diversity of their 

 structure would substantiate this view. 



There has been some tendency among recent authors on the 

 Microsauria, including the present writer, to class them with the 

 Reptilia. This may, in the future, be necessary, but not in the present, 

 condition of our knowledge. Dr. R. Broom in a letter to the writer 

 expressed very good ideas on the scheme by which to divide the 



