| 1887] : Geology and Paleontology. 839 
with the centrum of the vertebra. There are only three small 
lost. The ribs are two-headed, and are always connected 
. P| . . . 
_intercentra developed between the basioccipital and atlas, and 
_ the two next vertebrz. i ; 
p- abdominal ribs consist of a median piece just as in Sphen- 
Odon, to this one or two lateral pieces are attached on both sides. 
In Sphenodon there are two pairs of abdominal ribs connected 
With one pair of true ribs, in Ichthyosaurus only one. 
: The shoulder-girdle is only comparable with that of Spheno- 
: 
‘ 
‘ 
X 
sm 
a 
es 
ib 
a 
ir 
y 
don; the clavicles and interclavicles are very much alike; the 
scapula and coracoid resemble very much the same elements in 
_ young Sphenodons when they are still free. 
; m The pelvis of Ichthyosaurus is in a rudimentary condition; it 
‘Contains the three elements, but a comparison with other pelves is 
_ of no value. 
~ The limbs are specialized for the animal’s life in water from 
_ Some land-living form, as I shall show. 
a The limbs or paddles of the Ichthyopterygia were a principal 
ea for giving a peculiar position to those animals in the sys- 
. E have shown before, on logical reasons, that the paddles of 
. he yosaurus were not original but adapted. To-day 1 can give 
WE proofs for this. 
vi e Museo Civico of Milano, in Italy, are some specimens 
" Ichthyosaurus from the Trias of Besano. They have been 
med lately by Professor F. Basani, and called /chthyosaurus 
Th ote € specimens measure from 50 to go cm. only. 
ag teeth are of smaller number than in the other Ichthyosau- 
‘ment; and of two forms. But the most important character not 
and ‘ned by Basani is the structure of the limbs. Radius 
not 
"Presents nt, but the ulna; the ulna of Professor ‘Marsh 
_ The ie roly the pisiforme. 
hthyopterygia had few phalanges and not more 
© digits; radius and ulna were longer than broad, and 
eas Phalanges were developed, more digits 
a: division of 
57 
