58 
ICH TH Y OS A UR I A FROM THE 
Case. Shelf. 
IX 
Osteological 
X a 
X b 
b 
No. 
—14 Over Shelf a is an associated series of 14 
small thin vertebrse from the Galt of Ches¬ 
terton, apparently immature and not well 
preserved. 
Cervical to caudal. 
CABINET X. 
series illustrative of the modifications of the genus 
in the Cambridge Greensand. 
.—18 The basi-occipital bone of Ichthyosaurus. 
They may be referred to at least three 
species. In the larger forms the posterior 
aspect of the bone is sub-spherical; in the 
smallest it is transversely elongated. The 
large forms differ; some have the ex-occi¬ 
pital facets parallel to the neural canal, 
while in most those facets are concave 
from side to side and make a great angle 
with the neural canal. The condyle varies 
in form and in its ligament-markings. 
Atlas and axis, basi-occipital and basi-splie- 
noid bones. 
1 A large atlas and axis, pentagonal in form, 
with the sub-pentagonal posterior cup as 
large as the sub-circular anterior cup for 
the basi-occipital. The sutural line be¬ 
tween the bones is almost obliterated; the 
atlas is the thicker bone. The two infe¬ 
rior sides are flat and meet at a right 
angle. 
2 A small atlas and axis, with the sutural line 
distinct in the upper half of the specimen, 
showing the axis to be less than two- 
thirds the thickness of the atlas. The 
posterior cup is smaller than the anterior 
cup and much smaller than the transverse 
