VOL. XVI.(2) | INFERIOR-OOLITE ECHINOIDS 159 
It has also been recorded by the officers of the Geological 
Survey* from the Inferior Oolite of Castle Carey and 
Bruton. 
Except for these three echinoids, all the other species 
which are given in the above list are confined to beds of 
post-Garantcane date, and their presence in both districts 
is probably due to migration consequent on the disappear- 
ance of the barrier which separated the two districts during 
pre-Garantcane times. Some of the other species are 
also dealt with in section (3). The occurrence of Czdarzs 
Wright at Dundry Hill, and of Galeropygus agarictformis 
in Dorset, both of which species are characteristic of beds 
of Murchzsone date around Cheltenham, seems to indicate 
that some connection may possibly have existed at that 
time between Dorset, Dundry, and the Cotteswolds. 
(2) Forms restricted to a district, so far as ts known 
at present.—These are enumerated in Table IV. 
(3) Forms that have migrated from one district to 
the other.—In dealing with the question of the direction 
of migration, it is necessary to bear certain matters in 
mind. Chief among these are the size and relative abun- 
dance of the individuals of a species. For, in general, the 
size and number increase towards the source of distribu- 
tion. The horizons along which specimens occur most 
abundantly in different areas must also be carefully noted, 
since they will naturally occur at the lowest horizon 
in that area in which the species originated, and from 
which it migrated. 
In the present paper, the species that have migrated 
can be classed under two headings, namely, (i) those 
that have migrated from the Doulting-Stonesfield district 
southwards, and (ii) those that have migrated from Dorset 
northwards. 
1 “The Jurassic Rocks of Britain—The Lower Oolitic Rocks of England (Yorkshire 
excepted). Mem. Geol. Surv., vol. iv. (1894), p. 86. 
