PROSOBRANCHIATA. 339 
described (‘ Mag. of Nat. Hist.’ for 1837, p- 217) a recent species, V. De/te, in which the 
operculum is represented zw séfd, and this is spiral and horny. M. Bosquet has, 
however, figured a fossil found in the Limbourg Beds as Nematura pupa (‘ Reck. Paléont. 
Terr. Tert. du Limb.,’ 1859, p. 7, pli, 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, pl. xiv, fig. 15), and of which the late Dr. S. P. Woodward, in his ‘ Manual 
of Mollusca,’ p. 16, says, “This fossil appears to be a Limaz.” 
The following Fluviatile 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. Prrnarztia, Ldwards, 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.' 
Type. P. Rickmani, Edwards? 
2. Patupina, Lamarck, 1812. 
“ Operculum horny, irregularly concentric, having its nucleus on the inner side.” 
Type. Helix vivipara, Linné. 
3. Byruinia, J. #. Gray, 1821. 
“Operculum testaceous and solid, irregularly concentric, having its nucleus nearly in 
the middle.’ 
Type. Helix tentaculata, Zinné. 
?4. Amnicoua, 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. Avonicola Parkinsoni, Sandberger. 
1 Tn 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 ridges, 
though these are not very distinct. I think possibly it may have belonged to the above genus. 
* A shell resembling this generically is figured and described by Prof. Deshayes as Ampullaria 
problematica (‘An. sans Vert. du. Bas. de Par.,’ tom. xi, p. 521, pl. xxxvi, figs. 1, 2), and another, 
possibly the same species, is figured and described by Melleville in his ‘ Mém. sur les Sab. Tert. Infér.,’ 
p- 72, pl. x, fig. 1, as Buccinum arenarium. 
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