HaTCHIIK : AsiKOlJON IN Wvo.MiNf;. 13 



in plate XI.. of his Dinosaurs of North America as pertaining to Plciiro- 

 ca-lus nanus agrees very well. exce])t in size, with a similar fragment of 

 Brontosaunis ngured in plate XX. If one compares the detached 

 teeth oi Brontosaunis and .Istrodon {J'/eiiroc-a'/iis) as shown by Marsh 

 respectively on plates XX. and XL. of his Dinosaurs of North America, 

 he cannot hut be im])ressed with the remarkable similarity which they 

 exhibit. While it is true that .some of the remains described by Pro- 

 fessor Marsh as i)ertaining to Astrodon {P/ci/roca-Ii/s) could not pos- 

 sibly have belonged to a young Brontosaur, it is e(iually true that the 

 association of this material is purely conjectural. No two bones or 

 fragments of all that material collected from the Potomac beds in 

 Maryland were found in such relation to one another as to demonstrate 

 that they had belonged to the same individual. In any discussion as 

 to the affinities of the.se various genera and species of small .sauropod 

 dinosaurs, not only the innnature nature of the remains ujjon which 

 they have been based, but also the scattered and disarticulated state in 

 which they were found, must be constantly borne in mind. With the 

 possible exce])tion of Elosaiinis pat-viis it remains to be shown that any 

 of these forms are not the young of some of the well-known larger 

 forms, and most of the known remains of this last-mentioned genus 

 resemble very closely in many im])ortant details like parts of the skele- 

 ton oi Morosaunts, as has been pointed out by Peterson and Gilmore 

 in their original description. 



The discovery of these remains of Astrodon in the Jurassic deposits 

 of Wyoming is of the greatest importance as furnishing additional evi- 

 dence in favor of the reference of these two widely separated deposits 

 to one and the same geolo^cal horizon as was originally suggested by 

 Marsh. Should future discoveries demonstrate that any one, or all of 

 these smaller sauropods, are but immature representatives of the larger 

 forms, the evidence in favor of this correlation will be strengthened 

 rather than weakened. Marsh has reported remains of Astrodon 

 {F/euroca'lus') from the Jurassic deposits near Havre in Normandy, 

 while the type of Astrodon {Plenrocceius) si/ffosi/s was derived from 

 the Kimmeridge of Swindon, England. It is evident therefore that 

 these dinosaurs had a very wide geographical distribution and that 

 while the European forms may belong to different species than the 

 American they nevertheless furnish important evidence as to the rela- 

 tive age of the European and American deposits. Since the Kimmer- 

 idge clays are of undoubted Jurassic age, and considering the simi- 



