66 FAUNA OF THE CORNBRASH. 



Alaria, sp. incl. 



Besides the specimens above enumerated, which show the characters of both 

 the spire and the wing, there are others in which the latter is wanting and the 

 species of which cannot therefore be adequately determined. 



Family Cerithiid.e. 



These so-called cerites can only be denned as shells with dextral apex, of small 

 spiral angle and small body-whorls, with simple interior cavities. Scarcely as 

 much as this can be said of all the shells which are or have been included under 

 this title, yet the definition above given would include such shells as Terebra, 

 Turritella, and Scalaria. Fossil shells of such unspecialised character cannot be 

 definitely arranged in families by means of their forms alone. It is useless to 

 attempt to thrust the creatures of the Jurassic period into the pigeon-holes 

 prepared for the most part only at a later date. As has happened among the 

 Cephalopoda, the seat of variation has doubtless varied from time to time, and the 

 classification to be true to nature must vary likewise with time. 



Deslongchamps, who first studied the cerites of the Jurassic rocks, noted that 

 they had " a facies different enough [assez different] from that of living species 

 or of Tertiary fossils," but was unwilling to create new genera. He divided them, 

 however, into 6 groups — (1 a) whorls concave in the middle, intumescent at the 

 sutures (would now be called Aptyxiella) ; (1 b) whorls concave, raised at the 

 sutures (Gryptaulax) ; (2) whorls flat or subrotund (mixed, inc. Turritella) ; (3) 

 whorls round but not clathrate (Turritella ?) ; (4) clathrate, muricate (Bittium) ; 

 (5) longitudinally nodulose, series oblique from right to left (Gryptaulax ?) ; (6) 

 polygonate or tuberculate, one series perpendicular to the suture (various). Some 

 of these have channeled apertures and some have not. We cannot therefore include 

 the channeling of the aperture in the " family " character. 



The records of Cerithium are : 



*G. gemmatum (6, 28, 43), *G. muricatum (43, 48). 



*G. variabile (32, 37). 



For Cerithium gemmatum and C. millepunctatum see Bittium pingue, p. 67. 

 For G. muricatum see p. 68. Cerithium, variabile has been quoted from the Corn- 

 brash of Islip by Whiteaves, and thence quoted by Phillips ; but the only specimens 

 bearing that name are not in the collection of the former but in the Oxford Museum. 

 They are two poor casts only, and in any case there is a doubt, as has been noted 

 before, as to the horizon from which they were obtained. The species was called 



