50 GASTEROPODA OF THE INFERIOR OOLITE. 
which is enormously rich in large Cephalopods, though not quite so good for 
Gasteropoda as the top and bottom beds of the series. 
In the Department of Calvados there is a third bed where the ferruginous Oolites 
become scarce and less well defined. This is characterised by the abundance of 
Am. Niortensis and Am. Parkinsont interruptus, by large varieties of Plewrotomaria 
mutabilis, by Pl. bessina and Pl. scalaris, and by ** Turbo” duplicatus. Specimens of 
Terebratula spheroidalis are more abundant than in the second bed, and Ter. Phil- 
lipsit may be noted. This description probably fits better with our Cadomensis- 
bed (H;) than either of the other two with their presumed equivalents. The abund- 
ance of the peculiar group of Cosmoceras indicated by Am. Niortensis and Am. 
Parkinsoni interruptus is very suggestive, since this is exactly what we find in H, 
at Oborne. Just as coming events cast their shadows before, so did these pre- 
cursors of the grand army of Cosmoceras prepare the way for the reign of Am. 
Parkinsoni which was shortly to set in. 
Mitsorn Wick.—This is a roadside exposure, one and three quarter miles 
north-north-east of Frogden Quarry, where a peculiar phase of the Humphriesianus- 
zone presents itself. About nine feet of rock is exposed, of which the lower three 
feet are simply calciferous grits (Dew-beds). The ‘‘ fossil-bed ” is about eighteen 
inches thick, and consists for the most part of a softish white limestone, not unlike 
the marl with green grains at Oborne. In the upper part are numerous species of 
Spheroceras, whilst in the lower part Am. Humphriesianus and Am. Braikenridgii are 
not uncommon. Ter. spheroidalis occurs in the upper part of the fossil-bed. But 
few Gasteropoda are quoted from here. : 
Development of the Humpnrinstanus-zone in Dorset—Somerset.—A line drawn 
from near the town of Sherborne in a north-easterly direction to Milborn Wick 
(Somersetshire) is about three miles in length, and this line coincides with the 
principal development of these beds in No.1 District, a development by far the 
most important in England, though the zone is very well represented at Dundry. 
Henceforth, as we pass northwards into Somersetshire, the character of No. 1 
District undergoes considerable modification. 
Corton Down Quarry.—Between three and four miles due north of Sherborne. 
The Lower Division is again well represented here, since many specimens of 
Am. Murchisone are quoted. No traces of the Humphriesianus-zone were observed 
by me. 
Beyond this the exposures are lacking in interest from our point of view until 
we arrive in the neighbourhood of Castie Cary. To the south-east, east, and 
north-east of this town are three exposures in the Inferior Oolite, which have 
yielded a fair number of Gasteropoda. As this is a district but little known, the 
following particulars may be interesting. 
