academy op sciences.] PUBLISHED RESULTS. 133 



side. This is followed by a discussion of the origin of the sternum from the anterior ventral ribs 

 in the Amniota, for which the evidence, according to Williston, seems complete. 



The paper entitled "Synopsis of the American Permocarboniferous Tetrapoda," 1916, 131 

 is of the highest possible importance, for in it we have almost the last statement by Williston 

 concerning these forms which he knew as did no other. In commenting on his paper on 

 primitive reptiles, 1912, Williston says (p. 193) : 



The lists of constant characters [see p. 016] then given have been reduced, as I felt sure they would be, by recent 

 discoveries. * * * The final distinction between the two orders [Theromorpha and Cotylosauria] thus seems to 

 be limited to a single character, the absence or presence of the temporal perforation, a character which, it might be 

 urged, is not of supreme importance, though Broom considers the Cotylosauria a superorder. 



The following pages present a synoptic review of the generic, family, and ordinal characters 

 of the American Permocarboniferous Amphibia and Reptilia as Williston interprets them, in 

 the hope that it will serve as an inventory of our present knowledge, regardless of personal 

 views as to its taxonomic application. He does not attempt to characterize the various proposed 

 suborders of reptiles, because he does not know how to measure them, nor how to distinguish 

 them from families; nor is he at all sure, on the other hand, which are family and which are 

 merely generic characters. Illustrations of the more important types are included in the 

 summary. 



The skeleton of Trimerorhachis is again discussed in 1916. 129 The animal had been described 

 by Williston before, but now for the first time a connected skeleton has been found, through 

 which alone, as he had predicted, the ribs, tail, and feet could be made known. The creature 

 had the small limbs and broad neckless body of the modern Necturus, and Williston believes 

 that the type under consideration was an aquatic animal incapable of progression on land, 

 and in all probability, like Necturus, a perennibranchiate. 



Labidosaurus is described in detail in 1917, 133 some half dozen very perfect specimens having 

 been found by Mr. Miller near the Craddock ranch in 1916. The sclerotic plates of the eye are 

 demonstrated and the entire skeleton shown, together with a flesh restoration. The peculiar 

 rakelike teeth of the premaxilla? are bent backward, however, so that they effectually lock the 

 lower jaw and would prevent its opening were that their position during life. An extremely 

 important paper on the phylogeny and classification of reptiles was also published in 1917, 134 

 and represents Williston's last published views in the matter of the relationships of the four 

 classes of terrestrial vertebrates, all expressed graphically and with great clarity in a table some- 

 what similar in general plan to the one published in 1909, although that was merely a table of 

 distribution in time and space while to the present one is added a graphic view of the phylogenies. 

 The 1917 table is here reproduced. 



His most primitive group he calls the Protopoda, including therein the upper Devonian 

 footprint, Thinopus, and subsequent forms known only from their tracks in the Mississippian. 

 From these he derives the Amphibia on the one hand and the Reptilia on the other, representa- 

 tives of each group being known from the Pennsylvanian, hence the inference that the division 

 occurred during Mississippian time. Of the reptiles, he recognizes four great divisions, the 

 Anapsida or Cotylosauria, Synapsida, Diapsida, and Parapsida, deriving the mammals from 

 the second and the birds from the third. His use of Osborn's terms is of interest, for he was 

 critical of them in earlier years (see p. 126). As he says (p. 413) : 



It was Cope who, years ago, first suggested that in the temporal region of the skull the surest criteria for the classifi- 

 cation of the Reptilia are to be found. Woodward carried the suggestion further, and showed their availability, but 

 it was Osborn and McGregor who first applied them definitely. They assumed too much, as we have seen, but the 

 credit is due to Osborn, more than to anyone else, for the foundation of a true reptilian phylogeny, and to him we owe 

 especially a better knowledge of the double-arched reptiles. lie has called them the Diapsida, and there is no better 

 name for them. After the elimination of the forms which we are sure do not belong with them, we are all now, I think, 

 in accord as to their phyletic unity. 



The group or subclass of single-arched reptiles, with due modifications of the original 

 concept, may properly bear the name Synapsida given to it by Osborn. It is the group that 

 gave origin to the mammals and has long since been extinct. The temporal opening which, as 



