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.

131

The paper entitled "Synopsis of the American Permocarboniferous Tetrapoda," 1916,13 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 premaxillæ 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 somewhat 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, representatives 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 classification 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. He 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

Williston believed, arose by the separation of the squamosal and jugal, and not by a definite perforation of any bone, is the sole character by which the group is ultimately distinguished from the Cotylosauria, its ancestral stock. What further phylogenetic work Williston did for his incomplete book on the Reptilia is not now evident to the reviewer. At present the paper under discussion forms the final published statement by one of the highest authorities.

But two papers other than reviews came from the press in Williston's final year, one on the evolution of vertebræ,136 the other, Part III of the "Osteology of some American Permian Vertebrates." 137 The first of these discusses the homologies of the elements of vertebræ, primitive and otherwise, with their evolution, and is of great value to the student. The other describes further the genera Eryops Cope, Chenoprosopus Mehl and Naosaurus Cope, differentiating the last clearly from the closely allied Edaphosaurus.

GEOLOGY.

In his geological writings, Williston merely discussed such formations as he was concerned with paleontologically, for he was, like most vertebratists, primarily a comparative anatomist, and concerned with geological matters largely as he was with geographical ones, merely from the standpoint of distribution. He wrote of the Kansas Chalk, of semiarid Kansas, of the Kansas red beds, a summary of Kansas geology for a popular work by Angelo Heilprin, on the Laramie (Lance) Cretaceous of Wyoming, on the red beds and Morrison of Wyoming, and finally, with Case, on the Permocarboniferous deposits of the Southwest.

MAN.

A number of papers on man came from the pen of Williston, again largely, one might say, as a by-product of his other research. They discuss chiefly the occurrences of prehistoric man in Kansas, and he records one of the few authentic instances of the occurrence of human artifacts with extinct animals in America. He also wrote two papers on human evolution, of which the second, on the birthplace of man, has already been alluded to as an address delivered before the Paleontological Society in 1909 (see p. 118).

SUMMARY.

The most notable results of Prof. Williston's research lie, aside from the insects, almost entirely within the groups of Amphibia and Reptilia of the Paleozoic and Mesozoic. Compared with the volume and worth of this research, his other work on the fishes, birds, and mammals is almost negligible. He taught, however, many biologic, anatomic, and taxonomic truths of far-reaching application, so that a student of vertebrates of any class, either recent and extinct, can not afford to overlook his results. He gave us much that we know of the fauna of the Cretaceous, notably of the pterosaurs, plesiosaurs, and mosasaurs, and to him we also owe a very large part of our exact knowledge of the Paleozoic air-breathers, for his indefatigable work in the field and laboratory, aided by a few, very devoted co-laborers, has brought to light a fauna amazing in its extent and degree of perfection-entire skeletons of forms many of which were either new to science or known in very fragmentary condition. Williston not only gave a very clear understanding of the osseous morphology of the forms under consideration, throwing much light upon such vexatious problems as the homologies of the cranial elements, of the individual vertebræ, and of the amniotic sternum, but by careful comparative study of existing forms was enabled to restore his creatures in the flesh in a way that, anatomically at least, is thus far above criticism. He discussed at some length the life conditions, feeding and other habits, prowess, and evolutionary adaptations of the forms which he studied, and his knowledge was such that he could generally recognize such resemblances as were the result of convergence and such as actually implied a like heritage. His ideas concerning the phylogenies of the amphibian and reptilian groups developed somewhat slowly, due to his desire that such should be founded upon a considerable body of attested fact. In his final paper on phylogenies, in 1917, he

acknowledges, as the best that we have, those broader groupings of such men as Osborn, whose work he was inclined to criticize most emphatically when it first appeared 15 years before.

Williston laid a broad and fundamental foundation for the fabric of our knowledge concerning the cold-blooded air-breathers, building solidly and securely much of the superstructure as well. It is doubtful whether later students of the reptiles particularly will find much that is amiss, especially when the last work of the master shall have been published posthumously. On the other hand, it is the writer's belief that they can build thereon fearlessly, knowing that that which has been done is secure..