32 GASTEROPODA OF THE INFERIOR OOLITE. 
Gasteropoda on this line to entitle it to the dignity of an “ Univalve Bed.” The 
fossils are mainly those characteristic of the Lower Division, and more especially 
of the Murchisone-zone; e.g. Cirrus, usually a fossil of a low horizon. The other 
Gasteropoda from here will be named in their due places. The upper portion 
of this in all probability shades off into the concavus-beds, or so-called Sowerbyi-zone, 
but as there are no special traces of Gasteropoda here we need not go further into 
the inquiry. There are signs of the so-called “ Sowerbyi”-zone in a quarry 
on the north side of the Bredy, but I found no Gasteropoda there of any conse- 
quence. 
Again, the line between the Lower and Upper Divisions of the Inferior Oolite 
cannot be laid down to an inch or two with absolute certainty in the cliff section. 
This doubt arises mainly from the feeble and imperfect development of the 
Humphriesianus-zone, a failure very characteristic of South Dorsetshire. As far 
as an inspection of this section goes there seems to be no independent development 
of the Humphriesianus-zone at all otherwise than as an adjunct to the rich-shell at 
the base of the Parkinsoni-zone (P,). This was noticed by Oppel, who, whilst 
alluding to the trifling thickness of the Inferior Oolite, speaks of the fossils of the 
Humphriesianus- and Parkinsoni-zones being found together in one and the same 
bed of Oolite. To a certain extent this is so, and if such a zonalist as Oppel 
admitted the fact the evidence in its favour must be very strong indeed. 
We have then to consider the character of the shell-bed which I have distin- 
guished as P;. It is mainly situated towards the lower portion of the third block 
of limestone, and is by far the most important shell-bed in the Burton Bradstock 
Cliff. A portion of it also belongs to the next block, the split taking place through 
the midst. The result is that when the larger blocks break up there is a double 
surface presented to the collector’s chisel. Astarte obliqua is very abundant, and 
there are also other species of Astarte, so that this is sometimes known as the 
Astarte-bed. The upper part of P, is crowded with 7. spheroidalis, whilst in 
the lower part the Astarte is most abundant. It is in this lower part that the 
Gasteropoda of this shell-bed principally occur. Specimens of moderate-sized 
Am. Parkinsoni are by no means uncommon in the Astarte division of P), and may 
be found quite down to the base of the shell-bed. Sometimes, however, in the 
very base of the bed, and in that portion which belongs to the lower block, fair- 
sized specimens of Am. Humphriesianus, or a very closely allied Stephanoceras, may 
be found. It is just possible that there may be a slight unconformity between the 
two lines so that, here and there, specimens belonging to an older and lower zone 
are sometimes adherent to the main mass. In this way an uncompromising 
zonalist might seek to explain the apparent admixture. However that may be, it 
is perfectly certain that specimens of Am. Parkinsoni are to be found quite as low 
as any of the Gasteropoda hereafter to be described, and therefore I have no hesi- 
