448 The American Naturalist. [May, 
Diplodocus—In Diplodocus and its allies the sacral ribs are 
not intervertebral, but are connected with the centra of the 
vertebre only, without diapophyses. 
Ceratosaurus—In Ceratosaurus and its allies the sacral ribs 
are intervertebral, but entirely free from the well-developed 
diapophyses, which also support the ilium. The diagrammatic 
figures show these gelations. We see also that the structure of 
the sacrum shows greater differencés than we find in a natural 
group, and also shows that the Dinosauria must be given up. 
: II. THE SHOULDER GIRDLE. 
In the shoulder girdle we find, as in all Archosauria, a simple 
coracajd and an elongate scapula. So far no clavicles have been 
found, and I think that these elements are absent in Iguanodon 
and Diplodocus and the allied forms, but I should not be surprised 
at all if further discoveries would demonstrate the presence of 
_ clavicle and interclavicle in the megalosauroid forms. 
IV. THE PELVIS. 
Iguanodon.—The pubis of Iguanodon and its allies at once 
distinguishes it from all the other groups. As is well known and 
now shown without doubt, the ectopubis or pectineal process in 
this form is exceédingly developed; the entopubis or true pubis 
being directed backwards This character alone is sufficient to i 
separate Iguanodon far from Diplodocus and Ceratosayrus. In 
the highest specialized members of the Iguanodon group— 
Agathaumas (Triceratops), for instance—the ectopubis is enof 
mously developed, the entopubis being quite rudimentary. oe 
Diplodocus—Here we have the pubis directed forwards, and cs 
pierced by the obturator foramen, all the bones of the pelvis 
being very massive. a eee 
Ceratosaurus.—Also in this form the pubes are directed for- 
wards, but are closely united at the distal two-thirds, appe™ g G 
like a chevron bone when seen from front; also the ischia n : 
united at the distal end; the elements of the pelvis being ende se pi 
It is evident that Diplodocus and Ceratosaurus T 
other very much more in the structure of the pelvis than they % geet 
