332 GASTEROPODA OF THE INFERIOR OOLITE. 



Genus — Nerita, Linnaeus, 1758. 



Systematic conchologists, such as Fischer, do not carry the genus Nerita so far 

 back in time as the Jurassic period. That author (' Manuel,' p. 800) observes that 

 the Jurassic forms of Nerita are doubtful and belong to the genus Neridomus, Morris 

 and Lycett. Accepting provisionally the classification of these authors for the 

 Neritoid shells of the Lower Oolites, I think that Nerita will cover the more rugose 

 and costated forms with flattened inner lip, though, as far as my experience goes, 

 there is no denticulation of the edge. Viewing Neridomus as a section of Nerita, 

 this will include shells which are smooth and have the inner lip convex. It has 

 always seemed to me that Neridomus was more nearly related to Neritina than to 

 Nerita. Cossmann, I may remark, is disposed to query the value of the generic 

 distinction between Neritina and Nerita, and he has no hesitation in placing all the 

 Nerite-like shells of the Jurassic rocks under Nerita} 



As a matter of fact, I distinguish in our Inferior Oolite three rugose and costated 

 forms, which no doubt are closely related, and more or less run into each other. 

 There are also two, if not three, fairly distinct smooth forms which belong to the 

 section Neridomus, besides some others which are too obscure to notice. 



265. Nerita costulata, Beshayes, 1838. Plate XL, figs. 6 a, 6 b ; and ? Plate 



XXVIII, figs. 6 a, 6 b. 



1824. Neeita costata, Sowerby. Min. Conch., pi. cccclxiii, figs. 5 and 6. 



1838. — costulata, Deshayes. Lamarck, Anim. sans Vert., 2nd edit., 



vol. viii, p. 617. 

 1851. — — — Morris and Lycett, Great Ool. Moll., pt. i, 



p. 57, pi. viii, fig. 6. 

 1884.? — — — [var.] Hudleston. Geol. Mag., dec. 3, vol. i, 



p. 299, pi. ix, fig. 10. 

 1885. — minuta, Sow. Cossmann, Et. Bath., p. 154, pi. xiii, figs. 30, 31. 



Bibliography, Sfc. — There has been much trouble in regard to the synonymy of 

 this well-marked species, first described by Sowerby from the Great Oolite of 

 Ancliff. But it seems to me that this confusion has been intensified through the 

 view taken by d'Orbigny in the ' Terrains Jurassiques ' (vol. ii, p. 231) that 

 Nerita minuta, Sow., is the young stage of the costate species. I quite agree that 

 Morris and Lycett were not correct in their identification of Sowerby's Nerita 



1 ' Etage Bathonien,' p. 151. 



