400 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 23, 
include Avicula cygnipes, Waldheimia perforata, Cidaris Edwardsii, 
and some others ; but their number is not so great as is usually 
supposed. The tendency among paleontologists to name every 
smooth punctated Lima, L. punctata, every scalariform striato-nodu- 
lose Plewrotomaria, P. similis, or every planulate Cryptema, C. ex- 
pansa, leaves no doubt that two species are often included under one 
denomination and that the numbers in common between the Lower 
and Middle Lias are doubtless fewer than is generally stated. I find, 
in the majority of cases, that the species cited from the Lower and 
Middle Lias belong to sectional groups, the species composing which 
have a general resemblance one to the other, and the differential 
characters cannot always be recognized at a glance. Of the many 
examples of the genus Cryptenia from the Lower Lias that I have 
examined, not one is referable to C. expansa, which is quoted from 
that formation. It is possible that some species of the zone of A. 
raricostatus may have been mingled with those of the overlying 
stratum during the period of its deposition; the similarity of the 
included matrices prevents a determination of the source of such 
presumed derivative fossils. 
It may reasonably be urged that as the faunula of the zone of 
Ammonites Jamesont forms an integral part of the fauna of the 
Middle Lias, and that as the species belonging to the zones of Am- 
monites raricostatus and A. owynotus present nearly as great affinity 
to those constituting the fauna of the Middle Lias as they do to 
those of the Lower Lias, the line of demarcation between the Middle 
and Lower Lias should be drawn between the zones of Ammonites 
obtusus and A. ovynotus. This arrangement would give a total of 
one hundred and sixty-four species for the united zone, seventy- 
eight peculiar, fourteen from lower horizons, and sixty passing to 
higher beds of the Middle Lias. But many of the species which, in 
the Gloucestershire area, are restricted to the zones of Ammonites 
oxynotus and A. raricostatus, are elsewhere associated with indubit- 
able Lower Liassic species in strata which, though superior to the 
“ Bucklandi-beds,” do not admit of a division into zones of life; and 
it is not certain whether these strata, which may be designated as the 
Belemnite beds of the Lower Lias (or the zone of Belemnites acutus), 
represent the whole of the beds superior to the zone of A. Buck- 
landi, or whether only a portion of the upper series is present. 
Beds of this character occur in Shropshire, near Bath, at Ballintoy, 
Co. Antrim, in the east of France, &c. 
It is not my present intention to discuss the paleontological 
affinities of the whole Lower Lias and Middle Lias, which I reserve 
till such time as the claims of the so-called recurrent species have 
been fully investigated ; but so far as the distribution of species in 
the uppermost beds of the Lower Lias, and in the lowest horizon of 
the Middle Lias is concerned, there appears to be a paleontological 
unconformity between the Lower and Middle Lias as herein defined. 
If this be true, then the lithological conditions will justify me in 
suggesting a break in the stratigraphical succession. It is a received 
axiom that a change in lithological conditions is accompanied by 
