12 AXXALS OF THE CaRNEGIE MuSEUM. 



were found in essentially, and perhaps identically, the same locality and 

 horizon, and, in consideration of the very great similarity which they 

 exhibit, there a]:)pears no good reason for considering them as pertain- 

 ing to either different genera or species. Astrodon joluistoiii Leidy 

 ha\ing priority should therefore be retained, while Plcurocirhis Jia/iits 

 would become a synonym of that genus and species. 



Relations of Astrodon johnstoni Leidy (Pleurocct.lus nanus 

 Marsh) and Elosaurus parvus Peterson and Gilmore to 



OTHER genera OF JURASSIC SaUROPOD DiNOSAURS. 



It will have been noticed no doubt that the character of the remains 

 which have been referred to the above-mentioned genera and species 

 indicates that they pertain to animals not yet fully adult. This is 

 shown by the sutural connections exhibited between the centra and 

 neural arches of the various vertebrae ; by the free coracoid in Elosaurus ; 

 and by the character of such portions of the skull of Astrodon as have 

 been recovered. While collecting in the Potomac beds I secured a 

 number of fragments of skulls pertaining to both upper and lower jaws. 

 Whenever teeth were present they invariably belongeei to the first series 

 and were not yet fully erupted, the points of the crowns scarcely rising 

 above the borders of the jaw, showing conclusively that the animal had 

 not yet reached the adult stage. Some of the larger limb bones from 

 Maryland described by Professor Marsh as Pleuroavhts altus ^ may per- 

 haps have pertained to fully adult individuals, but unfortunately only 

 the tibia and one or two other fragmentary limb bones of this is known. 

 Now it would seem somewhat remarkable that only immature specimens 

 of these animals should have been secured while for the most part only 

 fully adult representatives of such genera as Diplodocits, Morosaurus, 

 Brontosauriis, etc., are known from the same deposits. Since these 

 last-mentioned genera must have been represented by young and im- 

 mature individuals it does not seem at all improbable that some of the 

 remains which have been referred to Plcitroavlus, Astrodon, or Elosau- 

 rus may in reality belong to the young of some of these genera of the 

 larger sauropoda. From what we know of the cervicals and dorsals of 

 Astrodon {^Pleurocxlus') they might very well have belonged to a young 

 specimen of Brontosaurus as might also the detached teeth figured by 

 both Leidy and Marsh ; while the fragment of a jaw figured by Marsh 



Kim. Jouni. Sri., Vol. XX.W, 1 888, ]i. 92. 



