CHAP, X.] CONTINUITY OF THE CHALK. 487 
from the coast of Portugal more nearly allied to 
chalk forms than to any others, but it is in the 
Echinodermata that the peculiar relation between 
the ancient and the modern faunze becomes most 
apparent. ‘To review briefly the chief points bearing 
upon this question. The Apiocrinide, the group of 
fixed crinoids which I have already described, are 
abundant throughout the whole range of the Jurassic 
rocks, their remains being frequently very abundant 
in the thick cream-coloured limestone beds of the 
oolites. Towards the close of the Jurassic period, 
the typical genera disappear, and in the chalk we 
find the group represented by an evidently degenerate 
form, Bourguetticrinus. In some tertiary-beds frag- 
ments of the stems of a small Bourguetticrinus have 
been found, and such were likewise discovered in 
the recent lime breccia of Guadaloupe, which con- 
tained the well-known human skeleton now in the 
British Museum. There can be little doubt that 
these tertiary and post-tertiary fragments are to be 
referred rather to the genus Rhizocrinus, which we 
now know to be so widely distributed, living, in 
deep water. Now in this series of Apiocrinidee, 
extending from the Forest marble to the present 
time, although there is a succession of constantly 
changing species, yet the gradual degradation in 
development in the same direction throughout the 
series seems to point unmistakeably to some form 
of continuity, to a type gradually succumbing to con- 
ditions slowly altering in an unfavourable direction. 
The other family of the stalked crinoids, the 
Pentacrinide, are in a different position. They are 
abundant in the Lias; very abundant in the lower 
