56 



MEMOIRS OF THE CARNEGIE MUSEUM 



which later discoveries have shown to be erroneous. The material was from Canon 

 City, Colorado, and was collected by Dr. S. W. Williston. 



A second species, based upon material collected by Professor Arthur Lakes, at 

 Morrison, Colorado, was described by Marsh as D. lacustris in the same journal for 

 February, 1884, page 166. He simply characterizes it as of smaller size and with 

 more slender jaws. It is very probable that the Sauropoda, like the CrocodiUa and 

 most other Reptilia, continued to grow throughout the entire life of the individual, 

 and that their immense size is indicative of a very long life. It would thus appear 

 that size alone is an exceedingly unsatisfactory character from which to describe or 

 determine species among these animals. Moreover, we have elsewhere spoken of the 



remarkable asymmetry exhibited in the 

 same vertebra and of the marked contrast 

 in form of the adjacent vertebrae in the 

 same series, all of which cJiaracters indi- 

 cate a considerable individual variation 

 among the Diplodocid£e. Nevertheless 

 there are certain structural differences 

 that hold good with little variation 

 throughout certain parts of the vertebral 

 column in the known skeletons of Dip- 

 lodoGus that may with reason be considered 

 as of at least specific importance. Such, 

 for instance, are the direction of the 

 spines of the caudals, as exhibited in the 

 American Museum specimen and figured 

 by Osborn and reproduced here. These 

 in the American Museum skeleton, except 

 in the extreme posterior portion of the tail, rise almost directly upward instead of 

 being directed regularly upward and backward as in Nos. 84 and 94 of the Carnegie 

 Museum collections. Compare Pis. XII. and XIII. Also the great disparity in 

 the relative size of the cervical ribs as exhibited in our skeletons (Nos. 81 and 94) 

 and as figured by Marsli in his description of D. longus are certainly of specific im- 

 portance, as will be shown b}^ a comparison of Fig. 24 (after Marsh) with the 

 cervical series shown in PI. III. The free spine of the third sacral in No. 94 might 

 perhaps be also considered as of specific importance, although I am inclined to 

 believe it more probably due to the somcAvhat younger age of the individual as 

 indicated by its smaller size. 



Fig. 24. Cervical vertebra of Diplodocus Ion 

 gus Marsh. One eighth natural size. Aftei' Marsh, 



