R. F. Tomes—On Heterastrea, Lower Lias. 207 
Tt will be seen, also, that of the locally extinct Mollusca, as in the 
ease of the Mammalia, some are distinctly northern, some southern 
forms, and some have an extensive range from north to south. Con- 
sidering the wide distribution of the forms, both extinct and living, it 
is not safe, without taking into account the habitat and range of every 
species, to generalize upon the climatal conditions of the age. The 
collective evidence which we gain from the Mollusca as to the 
climate of the period is more reliable than that offered by the Mam- 
malia, because the various northern and southern Mammals could 
migrate to and fro with the changing seasons; but the molluscs 
once having found their way to a locality would remain there until 
they were “slowly driven away by unfavourable conditions. The 
two shells of most pronounced southern origin, Corbicula fluminalis 
and Unio litoralis, being fresh-water forms, Sonia not be affected by 
changes of temperature so soon as land-shells. 
With regard to geographical changes, the whole gravel fauna seems 
to point to continental conditions, when Europe was connected 
with Africa, and England was united with France and Belgium. 
The formation of the British Channel would put an end to the 
migration of the larger animals, and would cut off the species, which 
had here reached their furthest limit, from the region of their greatest 
development. These species, being thus isolated, would in time 
give way to the more vigorous forms, which were better fitted to 
their surroundings, and would not be affected by such changes. 
I].—On Hererastr#z4, A NEW GENUS oF MADREPORARIA FROM 
THE Lower Ltias. 
By Roserr F. Tomss, Esa. 
(PLATE VII.) 
URING the interval of ten years which has elapsed since my 
paper on Liassic Madreporaria was read at one of the meetings 
of the Geological Society, a great many specimens of Liassic Isastree 
and Septastree, chiefly from the Vale of Evesham, have come into 
my hands, and with this abundance of material I have examined 
anew the several species, and have arrived at the results contained in 
the present communication." When making these examinations, I 
have been invariably struck with the absence of a distinct and well- 
defined basal wall and epitheca. Further observation also showed 
that these Liassic forms differed from other Isastree in having 
occasional elongated calices, like those of Latime@andra. With the 
latter genus some of the Liassic Isastre@e@ were supposed (though as 
it now appears erroneously) to hold a near relationship, and one 
species received the (at that time) appropriate specific name lati- 
meandroidea. With this the supposed resemblance ended; for 
gemmation, which in Latimeandra is calicinal, was found to be always 
marginal in the Liassic forms.’ Fuller investigation brought to 
1 More than seventy specimens have been examined and contributed to the results 
made known in this paper. 
2 It has become necessary that gemmation in the genus Jsastr@a should receive 
further attention. It has been variously stated both by Prof. Duncan and by me to 
