CAMBRIDGE UPPER GREENSAND. 
67 
Cute. Comp. Drawer. Specimen. 
J / ii 
71—73 
74 
75—81 
and rounding into the free external sur¬ 
rounding side, which is short and rugose; 
sometimes the intervertebral articular 
surfaces of a centrum are so convex as 
to meet each other. Occasionally there 
is a slight indication of a small tubercle 
for a rib. These vertebrae are from the 
most flexible part of the tail, near to 
its termination. Beyond them the ver¬ 
tebrae are compressed from side to side, 
and elongated in antero-posterior ex¬ 
tent. Then the articular intervertebral 
surfaces again become flattened, and the 
vertebra is constricted in the middle, so 
as to be not unlike in form to the dorsal 
vertebra of a small crocodile. The 
neural arch is not preserved, but per¬ 
sisted nearly to the end of the tail. The 
smaller sets of bones are associated 
series. 
f. ii. 45, 47, 48 are worth examination 
from the concentric ridged markings on 
the articular surface, so noticeable in 
vertebrae of whales. 
J f iii 1—7 An associated series of bones of Ichthyo¬ 
saurus from the upper chalky part of 
the Cambridge Upper Greensand. They 
are imperfectly mineralized with phos¬ 
phate of lime, and have suffered from 
abrasion in the washing mill. 
iii. 1 is a large globose basi-occipital bone. 
The sub-circular saucer-shaped facets 
for the ex-occipital bones are below the 
plane of the neural canal, and appear 
to truncate it behind. Anteriorly the 
facet for the basi-sphenoid bone is 
divided into two equal lateral parts by 
5—2 
