658 



SCIENCE 



[N. S. Vol. XLI. No. 1061 



reduced to a percentage basis and these rela- 

 tive frequencies summed from the beginning 

 for each successive grade. The curves are 

 merely draughtsman's curves smoothing the 

 empirical frequencies, but for present pur- 

 poses they are quite good enough. 



Erom such curves one may read off at once 

 the relative frequencies of pressures of dif- 

 ferent grades. Thus for the Cold Spring 

 Harbor series fifty per cent, of the pressures 

 are about 10.5 atmospheres or lower, whereas 

 in the Desert series fifty per cent, of the 

 pressures are 15.7 atmospheres or higher. In 

 the Tucson series about thirty per cent, of the 

 concentrations are the equivalent of over 20 at- 

 mospheres, whereas in the Cold Spring Harbor 

 series only about three per cent, of the cases 

 exceed this value. 



Note also that in the Desert there is a 

 higher maximum and a higher minimum than 

 in the more mesophytic habitat. The range 

 of variation is also far greater in the Tucson 

 than in the Cold Spring Harbor series. 



In using cryoscopic methods we have so far 

 failed to find pressures so high as those re- 

 corded by Fitting. We are not, however, 

 ready to suggest that they do not occur. Pos- 

 sibly our failure to demonstrate them in the 

 Tucson region may be due to the fact that our 

 determinations were carried out at the close 

 of the winter and spring rainy season, and 

 hence on plants which had not been subjected 

 to the maximum dryness of the region in 

 question during the growing season of the 

 year in which the determinations were made. 



J. Arthur Harris, 

 John V. Lawrence, 



EOSS AlTKEN GORTNER 

 ON THE GENUS TRAOHODON^ 



In 1902 Mr. J. B. Hatcher published an 

 article^ entitled " The Genera and Species of 



cooling, by the use of tables already published. 

 See Harris and Gortner, Amer. Jour. Bot., 1: 

 1914. 



1 Published with the permission of the Director 

 of the U. S. Geological Survey. 



2 Annals of the Carnegie Museum, Vol. I., 1902, 

 pp. 377-386. 



the Traehodontidse (Hadrosauridse, Claosau- 

 ridse) Marsh," in which the conclusion was 

 reached 



that the ten genera [of the Traehodontidse] which 

 have been proposed should be reduced to two. 

 Trachodon Leidy and Claosaurus Marsh, while the 

 remaining eight genera should be treated as 

 synonyms of Trachodon, which should also be 

 made to include T. {Claosaurus) annectens Marsh; 

 while the smaller Claosaurus agilis described by 

 Marsh from the Kansas chalks [Niobrara] may 

 still be considered as pertaining to a distinct 

 genus. ' ' 



These conclusions were almost unanimously 

 adopted by American vertebrate paleontol- 

 ogists in their subsequent work, and this gen- 

 eral use of the term Trachodon has continued 

 up to the present time. 



The finding of more perfect material in re- 

 cent years has shown that several of the species 

 formerly referred to Trachodon represent dis- 

 tiact genera, and in the light of these dis- 

 coveries Hatcher's reduction now appears to 

 have been too radical, but he was probably 

 correct in restricting Claosaurus to the single 

 species from the Niobrara formation. 



It is unfortunate, however, that this view 

 of the genus Trachodon, which includes spe- 

 cies from the Judith Eiver formation to the 

 close of the Lance, has become so widely 

 accepted by paleontologists. 



In the first place the type of the genus 

 (Trachodon mirdbilis Leidy) is from the 

 Judith River formation and was founded upon 

 inadequate material consisting of " specimens 

 of teeth generally very much worn and in a 

 fragmentary condition," so that it is quite 

 impossible to identify positively with them 

 better and subsequently discovered specimens. 



That later Hatcher^ appreciated this fact 

 is clearly shown by the following extract: 



Although the trachodonta are easily distinguish- 

 able by their teeth from the other Dinosauria of 

 these beds [Judith Eiver] it is scarcely possible to 

 identify the various species of this genus or the 

 genera of the family from the teeth alone. 



Even though it eventually be found that 



s T. W. Stanton and J. B. Hatcher, • ' Geology 

 and Paleontology of the Judith Eiver Beds," Bull. 

 257, U. S. Geol. Surv., 1905, pp. 96-97. 



