December 11, 1896.] 



SCIENCE. 



865 



some sort. Whether the particles which 

 remove the charge come from the air, or 

 from the condensed gaseous layer, or from 

 the material of the body itself, is still in 

 dispute. It appears to me that the mass 

 of the evidence is in favor of the latter 

 hypothesis. But the possibility that the 

 phenomena may be complicated by elec- 

 trolytic conduction in the medium sur- 

 rounding the charged body,* must not be 

 forgotten. 



Ernest Merritt. 

 Cornell University. 



(To he concluded.^ 



THE NORTH AMERICAN ORIGIN OF-THE 



EDENTATES.f 



The explorations of the American Mu- 

 seum Paleontological party in the basin of 

 the San Juan, New Mexico, during the past 

 summer secured, among other important 

 materials, the larger part of the anterior 

 limb of Psittacotherium multifragum Cope, as- 

 sociated with the lower jaws and a number 

 of the upper teeth. The specimen in ques- 

 tion was found by the writer, and, with the 

 exception of a few unimportant weathered 

 fragments, was bedded in its original matrix, 

 a soft, friable, reddish colored clay. The 

 jaws and limb were not more than a foot 

 apart, so that there can be very little doubt 

 that they belong to one and the same indi- 

 vidual. 



It has been the custom of paleontologists 

 to place the genus Psittacotherium, after Cope, 

 in the Tillodontia, but it can now be shown 

 that it not only does not belong in this 

 group, but that together with Hemiganus, 

 Ectoganus and Stylinodon forms a closely con- 

 nected consecutive series ancestral to and 

 leading directly to the Gravigrada, or ground 



*In an early paper Arrhenius [W. A. 32, 545; 

 33, 638. Phil. Mag. 28, p. 75] suggested that the 

 air conducted electrolytically under the influence of 

 ultra-violet rays. 



tBull. Amer. Mus. Nat. Hist., Art. XVI., 1896. 



sloths. A second series, composed of Ony- 

 chodectes and Conoryctes, is clearly an allied 

 group, which probably gave origin to the 

 Armadillos. 



These two series I have arranged under a 

 new suborder for which I have proposed 

 the name Granodonta, and considered them 

 as constituting a primitive division of the 

 Edentata. 



This suborder has been defined as fol- 

 lows : ' * Primitive Edentates characterized 

 in the earlier forms by rooted teeth with 

 divided fangs, having a more or less com- 

 plete enamel investment ; in the later forms 

 by the teeth becoming hypsodont, rootless, 

 of persistent growth, and by limitation of 

 the enamel covering to vertical bands in 

 progressive decrease. By the presence of 

 incisors in both jaws, by a typical molar and 

 premolar dentition, by a trituberculate 

 molar crown, which disappeared early in 

 life through wear, leaving the dentine ex- 

 posed." 



The evidence of the Edentate affinities 

 of these forms is displayed most strikingly 

 in the Hemiganus, Psittacotherium, Ectoganus 

 and Stylinodon series in the following char- 

 acters : (1) The enlarged teeth in the front 

 of both upper and lower jaws can now be 

 determined as being canines, and not in- 

 cisors, as has formerly been supposed. In 

 the earliest genus, Hemigarius, from the lower 

 Puerco, the lower canine had already lost 

 the enamel from its posterior face, while the 

 crown of the upper canine is completely 

 encased in enamel ; the teeth were rooted, 

 having divided fangs, and the crowns of the 

 molars and premolars in the single speci- 

 men known are enamel- covered. (2) In 

 the succeeding genus, Psittacotherium, from 

 the upper Puerco, the superior canines 

 had also lost the enamel from the posterior 

 face, the roots of the lower molars and pre- 

 molars were connate, while the roots of the 

 upper molars were more or less divided into 

 fangs. The crowns of the molars early lost 



