29 
vo MEMOIRS OF THE CARNEGIE MUSEUM 
with the basioccipital. These elements are smaller than the homologous parts of 
B. marshi and B. discus and are hardly more than half the size of B. robustus. 
They differ in several minor characteristics. The atlas resembles B. marshi and B. 
robustus in having a single hypapophysis on the lower anterior surface of the cen- 
trum. The third and fourth cervicals differ from the same elements of B. marshi in 
having well developed parapophyses, and very small diapophyses. 
There is no indication of the parapophysis on the axis as found in both B. 
marshi and B. discus. Just below the diapophysis and separated from it by a non- 
articular tract is a faint antero-posterior ridge, which anteriorly probably represents 
1. 
Fic. 6. Atlas, axis, third, and fourth Fie. 7. Lat- 
cervical vertebrze of Baptanodon natans (No. eral view of in- 
1441). One half natural size. 1. Coalesced tervertebral disk 
atlas and axis. 2and 3. Third and fourth of  Baptanoden 
cervicals. d., diapophysis; p., parapophysis; (No. 1441). One 
z., hypapophysis. half natural size 
the rudimentary parapophysis of the atlas. Midway between this ridge and the 
lower border is a small vertical eminence not observed in the other species. The 
upper arches of these vertebree are not sufficiently well preserved to be described 
here. The other vertebree preserved appear very similar to the corresponding 
elements in the other members of this group. 
Intervertebral Disks.— Fig. 7 represents the shape and size of the matrix filling the 
space between the centra of the anterior vertebree. These biconvex disks are quite 
uniform in character and give an accurate idea of the thickness of the cartilage that 
once filled the spaces between the centra. The average thickness of the disks at 
their middle is about 30 mm. 
Anterior Limbs. 
About half of the proximal portion of one humerus was found. 
Fig. 8 shows the subrectangular outline of this articular end. The surface of this 
