4 BRITISH JURASSIC GASTEROPODA. 
one which involves the most trouble and preparation. The second method, 
besides being the most feasible, has, moreover, been already inaugurated by Morris 
and Lycett in their description of the Great-Oolite Mollusca. Hence there exists, 
as it were, a sort of prescription to describe the fossils according to their horizons, 
and it therefore only remains to determine what divisions shall be adopted. On 
the whole I am inclined to think that it would be the most advisable to complete 
the description of the Gasteropoda of the Lower Oo.rTus, already so well begun. 
For this reason the Gasteropoda of the Inferior Oolite have been chosen to consti- 
tute the first memoir of the contemplated Monograph. 
It does not appear that many important additions have been made to the 
Gasteropod Fauna of Bathonian beds in England since the date of Lycett’s ‘ Sup- 
plement.’ Hence with the completion of the proposed ‘ Memoir on the Gastero- 
poda of the Inferior Oolite,’ the Gasteropod Fauna of the Lower Oolites will, in the 
main, have been exhausted. It would then become a question as to what should 
be the subject of the next memoir. 
If the Middle and Upper Oolites, from the Kelloway Rock to the Portland- 
Purbeck inclusive, were made the subject of a second memoir, complete as regards 
the Gasteropoda, considerable advantages in the way of comparison would ensue. 
This course is the more to be recommended, since there is a disposition to regard 
the so-called Middle and Upper Oolites together as one great series of the 
Jurassic system. Nevertheless the difficulties which present themselves in having 
to grasp such a wide extent of beds are considerable; for the number of collec- 
tions that have to be searched must be borne in mind, and how differently as 
regards synonymy the fossils are arranged in each. Nothing, it is true, can exceed 
the readiness with which the chief authorities of our public museums render all 
the facilities in their power; but in some cases the rules do not admit of more 
than an inspection, whereas everyone who has had any experience knows what an 
advantage it is to possess a fossil, even for a few weeks—to study it and to be 
thus enabled to determine its characters under various conditions of light. Hence 
the importance of making use of private collections. 
The Gasteropoda of the Liassic Rocks might possibly form the subject of a 
third memoir, and in this connection it would be a subject of considerable interest 
to ascertain how far the Gasteropoda of the Lias, and especially of the Upper 
Lias, resemble those of the Inferior Oolite. My belief is that they would be found 
to do so to a much greater extent than is generally supposed, though the Gaste- 
ropod Fauna of the Inferior Oolite in our country is much fuller than that of the 
Lias; many of the genera which attain to such an important position in the 
Inferior Oolite are prefigured in the Lias. These remarks more especially apply 
to the south-west of England. 
People who derive their impressions of the Faunas of two series of beds from 
