114 GASTEROPODA OF THE INFERIOR OOLITE. 



the anterior canal is short, indistinct, and scarcely reflexed. M. Cossmann 

 observes that out of forty-one species of Cerithia recorded from Bathonian beds 

 in France, probably not more than half really present the characters of Cerithium. 

 We might almost say the same of many species in our Inferior Oolite. But if we 

 were to remove them from that genus it would be necessary to make a number of 

 allied genera in order to receive each species. In the case of forms now existing 

 where the shell is well preserved and the animal can be put in evidence, such 

 multiplication of genera is justifiable, and is even necessitated by the enforcement 

 of the binomial system of nomenclature. To adopt this method where imper- 

 fectly preserved shells are alone obtainable is scarcely to be recommended. The 

 result is that Cerithium, as a Jurassic genus, is not exactly the same thing as the 

 recent genus, especially as now restricted. The Jurassic Cerithia have not the 

 anterior canal so well developed or so strongly reflexed, and in some cases the 

 canal is very poorly developed indeed, a defect which is aggravated by imperfect 

 preservation. 



It thus happens that species have been ranged under " Chemnitzia " which 

 ought to be classified under Cerithium. This leads to the consideration of a 

 question which is best discussed at the present stage, viz. what is to become of 

 " Chemnitzia." It is scarcely necessary to point out that D'Orbigny's " Chem- 

 nitzia " of 1850 and his " Chemnitzia " of 1839 refer to distinct groups of 

 shells. The " Chemnitzia " of 1850 is now very generally referred to Pseudo- 

 melania, Pictet and Campiche, a genus well represented in the Inferior Oolite, 

 which will be dealt with subsequently. D'Orbigny's original " Chemnitzia " 

 is now held to be a synonym of Turbonilla, Leach (vide Fischer, p. 789), a name 

 applied to a group of shells which are elongate, narrow, and many-whorled, the 

 whorls being slightly convex and usually costulated ; the aperture is simple, and 

 oval or subquadrangular. This genus is said to extend no farther back than 

 the Tertiaries. In the Bathonian of France, Cossmann refers no species to 

 " Chemnitzia." On the other hand, Gemmellaro, and after him Try on, accept 

 Chemnitzia, D'Orb., as a genus of fossil shells, divisible into the sub-genera 

 Chemnitzia, Rhabdoconcha, Pseudomelania, Oonia, and Microschiza. The four last 

 sub-genera evidently belong to the Pseudornelaniadse, and need not be discussed 

 here. There remains, then, Chemnitzia, D'Orb., as restricted, of which one of the 

 types is Chemnitzia (Tiirritella) undulata, Benz. The following is Gemmellaro's 

 diagnosis : " Shell elongate, composed of a great number of whorls transversely 

 (axially) plicated. Mouth oval, rounded or angular in front, confined posteriorly. 

 Columella straight or sometimes curved, and slightly incrusted. Lip thin and 

 sharp." 1 do not think that there are any species in our Inferior Oolite which 

 come within the above diagnosis. There are one or two cases where Cerithia, of 

 the section originally grouped by Deslongchamps under Melania, have the anterior 



