CERITHIUM. 143 
different. Ifthe diagnosis of Diartema were somewhat altered, it might be made to 
include the species here described as varicifera. 
This is another instance where the Aporrhaide of the Lincolnshire Limestone 
at Great Ponton show their affinity with Bathonian forms. 
Famtiy—CERITHIIDA. 
* Shell spiral, elongated, many-whorled, frequently varicose ; aperture channeled 
in front, with a less distinct posterior canal ; lip generally expanded in the adult.’— 
8. P. Woopwarp, 
The above diagnosis was no doubt formed so as to include both Nerinea and 
Aporrhais, both of which are now excluded. Fischer observes that the shell is 
very variable; the canal, generally short, becomes rudimentary and even disap- 
pears completely, as though to show in some sort the impossibility of separating 
the Siphonostomes and the Holostomes. He observes that the same modifications 
of the canal are observed in the Melaniide. I would here remark on the 
possibility of the more recent Melaniide having originated from some of the old 
Jurassic Cerithiide, or at least from molluscs of that age, which we group with the 
Cerithiidz. Most freshwater Gasteropoda are probably descended from genera 
which were once marine. 
In the Inferior Oolite the Cerithiide are well represented, though some genera 
are placed here with a query—Brachytrema, already described, is thus classified 
by many. The following genera are referred to this family. Cerithiwm, Adanson, 
Fibula, Piette, Ceritella, Morris and Lycett, Ezelissa, Piette, Cryptaulax, Tate, and 
Cerithinella, Gemmellaro. Of these Cerithinella, and possibly even Cryptaulaa, 
might almost claim relationship with the Turritellide. 
Genus—Cerrituium, Adanson, 1757. 
© Shell imperforate, turrited ; whorls numerous, narrow ; the last always shorter 
than those of the spire ; aperture oblong, semioval ; anterior canal short, oblique, well- 
marked ; lip more or less thickened.” —Abridged from Fiscuer. 
The Jurassic Cerithia cannot be judged by the same strict diagnosis as may be 
applied to existing species. A considerable group of fossil shells, many of them 
small, occur in our Liassic and Oolitic strata, to which the generic name 
Cerithiwm is applied. Some of these fossils are, perhaps, more like Bittiwm, where 
