128 SAMUEL WENDELL WILLISTON- LULL. iMBaovi ^^xvn, 



appearing at the close of the Jurassic and in the Lower Cretaceous, we find strong evidence of a community of faunas, 

 but with a striking absence, hitherto, of some of the smaller forms known from earlier times in the eastern continent. 

 The Upper Cretaceous again shows a belated arrival on the western continent of eastern types, after their advent or 

 even disappearance there. With the exception of certain Triassic marine types, we have no distinctively American 

 Mesozoic groups of air-breathing vertebrates, until we reach the Benton, Niobrara, and Pierre Cretaceous, all indi- 

 cating a continued, but possibly restricted, intermigration between the eastern and western continents during the 

 whole of Mesozoic times. * * * That the communication between the two continents in Fennsylvanian time 

 may have been by way of the North Atlantic region is not at all improbable. Indeed, taking into consideration the 

 close relationships known to exist between the European and American type[s] of this period, closer perhaps than 

 existed at any subsequent time during the Mesozoic, this more direct way of communication would seem very probable. 



Williston goes on to adduce evidence in favor of the belief of a southern communication 

 between Africa and South America and, during part or all of Mesozoic time, free commu- 

 nication between North and South America. He feels that there may have been one trans- 

 Atlantic bridge, the southern one, but that this was sufficient nevertheless to afford a means of 

 intermigration between both the northern and southern continents of the old and new worlds. 



The discussion of the relationships of the various amphibian, reptilian, and mammalian 

 groups in this paper gives expression to WiUiston's beliefs, some of which are most decided, 

 although his evidence is not always forthcoming. 



Another paper of the same year 88 was on the skull and extremities of Diplocaulus, a very 

 curious microsaurian from the Permian, with a head remarkably extended in its transverse 

 diameter. The paper is largely morphologic — the brief discussion of the taxonomic rank of 

 the group which Williston would make the family Diplocaulidce of the Microsauria. 



Two other papers, one on Pariotichus 89 and one on Trematops, 91 follow. Both forms are 

 from the Permian of Texas, and the partial result of the expedition to these beds sent out by 

 Chicago University during the autumn of 1908. The Pariotichus skeleton is of particular 

 interest because for the first time the natural skeleton of a cotylosaur is known, with all of its 

 bones in anatomical relations, scarcely a single one being disturbed by extraneous force in fossil- 

 ization; so that from it a clearer and more authentic description could be given than ever before. 



Seven genera of Permian reptiles are enumerated as pertaining to the Pariotichidre, he 

 having added one, Labidosaurus, to the original six included within the family by Cope. 



Trematops is also represented by an almost complete skeleton, this time of a rachitomous 

 amphibian curiously intermingled in situ with the remains of a cotylosaurian reptile. The 

 amphibian forms the type of a new genus and species, and has as its nearest ally the well-known 

 Eryops originally described by Cope, although its smaller size, greater slenderness, and head 

 structure separate the genera widely. 



Four papers on Permian vertebrates came from WiUiston's hand during the year 1910, 

 one of which ° 8 discusses the skull of the reptile Labidosaurus, while another 97 makes known in 

 detail the entire skeleton and armor of a remarkable new genus, Cacops, and to a lesser extent 

 another new genus, Desmospondylus, and erects two new families: Dissorophoridas to include 

 Dissorophus Cope and Cacops Williston, and Trematopsidae, based upon the previously described 

 genus Trematops. 



The material here described was sought and found in the "barren" deposits of the Permian 

 of northern Texas, which so rarely pay for exploration, but which, when they do, pay abun- 

 dantly in the degree of perfection of the material; for, as Case has observed, but one or two 

 specimens a season can be expected from these clay beds. Mr. Paul Miller discovered in 1909 

 a remarkable bone bed containing, according to WiUiston's estimate, 50 or 60 skeletons, with 

 not another indication of bone.in adjacent exposures of several hundred acres, save a few ounces 

 of fragments found a half mile away. The great majority of the skeletons belong to the genus 

 Varanosaurus Broili, of about the same size — that is, 4 feet in length; there is, in addition, a 

 femur of Desmospondylus, while all of the amphibian remains belong to Cacops. The skeleton 

 which is figured as the type of Cacops is unusually perfect and is mounted with great skill, 

 only certain of the phalanges being restored, together with the distal segments of the limbs 

 from the right side; it is, moreover, almost entirely one individual. 



