Prof. O. OC. Marsh—Comparison of Dinosauria. 205 
2. The comparative abundance of another family (Cetiosauride), 
nearly allied to the Morosauride, but, as a rule, less specialized. 
3. The absence, apparently, of all remains of the Diplodocide. 
A number of isolated teeth and a few vertebree of one immature 
individual appeared to be closely related to Pleurocelide, but this, 
for the present, must be left in doubt. 
Among the American forms of Sauropoda, the skull is now com- 
paratively well known in the principal families and genera. Bronto- 
saurus, Morosaurus, and Diplodocus, typical of their respective 
families, are each represented by several skulls, some of which are 
nearly complete, and characteristic portions are known of the skulls 
of other genera. 
The vertebra, also, and especially the pelvic arch, afford distinc- 
tive characters. By the latter alone, the Aélantosauride and Moro- 
saurid@ may be readily distinguished. In the absence of the skull, 
this is a point of importance in a comparison of Huropean with 
American forms. 
In the Atlantosaurida, the ischia are nearly straight, and when in 
position, extend downward and inward, meeting on the median line 
by a symphysis of the two ends, as in Crocodiles. In the Moro- 
sauride@, the ischia are twisted, and extend inward and backward, 
with the inner margins alone meeting each other on the median line, 
the ends being free.? 
All the ischia of Sauropoda known from Kurope appear to be of 
the latter type, although proportionally broader and more massive 
than those of the corresponding American forms. The ilia and pubes 
associated with these ischia agree in their main features with those 
of the American genus Morosaurus, so that there can be little doubt 
that the same general form is represented in both countries. 
A striking difference between the Cetiosauride and the allied 
American forms is that, in the former, the fore and hind limbs appear 
_ to be more nearly of the same length, indicating a more primitive 
or generalized type. Nearly all the American Sauropoda, indeed, 
show a higher degree of specialization than those of Hurope, both in 
this feature and in some other respects. 
The identity of any of the generic forms of Huropean Sauropoda 
with those of America is at present doubtful. In one or two 
instances, it is impossible, from the remains now known, to separate 
closely allied forms from the two countries. Portions of one animal 
from the Wealden, referred by Mantell to Pelorosaurus under the 
name of P. Becklesii,? are certainly very similar to some of the 
smaller forms of Morosaurus, especially in the proportions of the 
fore limbs which are unusually short. This fact would distinguish 
them at once from Pelorosaurus, and until the skull and more of the 
skeleton are known they cannot be separated from Morosaurus, and 
should be known as Morosaurus Becklesii. During the examination 
of this specimen, which is in the collection of its discoverer, Mr. 
S. H. Beckles, of St. Leonards, England, the author found, attached 
1 Diagrams showing typical ischia in these families and in the Cetiosauride were 
exhibited by the author when the paper was read. 
* Morris’s Catalogue of British Fossils, p. 351, 1854. 
