﻿PROSOBRANCHIATA. 



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described (' Mag. of Nat. Hist.' for 1837, p. 217) a recent species, N. Delta, in which the 

 operculum is represented in situ, and this is spiral and horny. M. Bosquet has, 

 however, figured a fossil found in the Limbourg Beds as Nematura pupa ('Reck. Paleont. 

 Terr. Tert. du Limb.,' 1859, p. 7, pi. i, fig. 6), and at fig. 7 he represents what he thinks 

 may be the operculum of this species, but which is quite different in form from the one 

 figured as recent, being in shape like Ancylus ? latus (F. Edwards, 'Eocene Moll.,' 

 p. 110, pi. xiv, fig. 15), and of which the late Dr. S. P. Woodward, in his ' Manual 

 of Mollusca, 5 p. 16, says, "This fossil appears to be a Limax." 



The following Eluviatile shells from the Lower Tertiaries of England may, I think, 

 be separated into genera or sectional divisions, as indicated by the operculum ; and had 

 I been able to continue this work, it was my intention to have done this. 



1. Pitharella, Edwards, 1860. 



" Shell subcylindrical ; spire obtuse, more or less produced ; aperture oval-oblong, 

 rounded in front, narrowed behind ; columella straight or very slightly twisted, arched 

 anteriorly ; outer lip simple, acute ; inner lip thickened." 



Operculum unknown. 1 



Type. P. Rickmani, Edwards? 1 



2. Paludina, Lamarck, 1812. 



" Operculum horny, irregularly concentric, having its nucleus on the inner side." 

 Type. Helix vivipara, Linne. 



3. Bythinia, /. E. Gray, 1821. 



" Operculum testaceous and solid, irregularly concentric, having its nucleus nearly in 

 the middle." 



Type. Helix tentaculata, Linne. 



?4. Amnicola, Gould and Haldemann, 1841. 



" Shell ovate-conical, thin ; spire acute, composed of a few rounded whorls ; aperture 

 small, oblique, and roundedly ovate ; lips continuous, simple. Operculum horny, spiral, 

 with few volutions." 



Type. Amnicola Parkinsoni, Sandberyer. 



1 In Mr. A. Bott's cabinet is a fossil which has the appearance of an operculum. This I intended to 

 have had figured. It is of an elongately oval or lanceolate form, and apparently with concentric ridge*, 

 though these are not very distinct. I think possibly it may have belonged to the above genus. 



2 A shell resembling this generically is figured and described by Prof. Ueshayes as Ampullaria 

 prollematica ('An. sans Vert. du. Bas. de Par.,' torn, xi, p. 521, pi. xxxvi, figs. 1, 2), and another, 

 possibly the same species, is figured and described by Melleville in his ' Me'm. sur les Sab. Tert. Infer.,' 

 p. 72, pi. x, fig. 1, as Buccinum arenarium. 



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