PULMONATA. 69 



a change in the ordinary conditions of temperature, and of the nature and supply of 

 food, will be attended with appreciable differences in the development, although not in 

 the organisation, of the animal ; and that these differences will be represented in, and 

 will modify the form of the shell. And to such a cause, perhaps, may be attributable 

 the distinction, trivial as it is, which, as we have seen, exists between the shell of 

 the living H. labyrinthica and those of its Eocene representatives. 



The identity in question exhibits an instance of a terrestrial species surviving 

 important geological changes, and prolonging its existence through geological epochs 

 of very great extent, but to the probable duration of which no approximation even can 

 be made and yet preserving its normal form almost without modification ; an instance 

 unparalleled, if, as will probably prove to be the case, the various forms of Terebratula 

 referred to the recent T. caput-serpentis belong to different species. 



Brogniart, ('Ann. du Museum d'Histoire Naturelle,' torn, xv, p. 380,) has de- 

 scribed a small trochiform Helix from the neighbourhood of Mans {H. Menardi), 

 which, in the general character of its lineation, resembles this species. It is, however, 

 larger ; and the whorls, although described as being " nearly equal," appear, from the 

 figure given, to enlarge more rapidly. The aperture is neither described nor repre- 

 sented, and it is impossible, therefore, to form any opinion as to the identity of the 

 shell with the present species. 



Size. — Diameter, 1-1 0th in.; elevation 1-1 0th in. 



Localities. — Hordwell Cliff; Headon Hill. 



No. 21. Helix sub-labyrinthica. F. E. Edwards. Tab. XI, fig. 4 a — c. 



H. testa minima, globoso-conicd, umbilicatd; spird elevatd, apice obtuso : anfractibus 

 sex, rotundato-convexis, gradatim majoribus, transversim lineatis : aperturd, obliqua, semi- 

 lunari, simplici (?); umbilico parvo. 



I possess only one specimen, and that merely a cast, of this small and very rare 

 Helix. Although more pupiform than H. labyrinthica, it approaches so nearly to that 

 shell that I feel great hesitation in referring it to a distinct species ; on examination, 

 however, differences appear which scarcely justify my describing the shell as merely a 

 variety. 



It is a small, globosely conical shell, with an obtuse apex, and formed of six 

 roundedly convex whorls, increasing in size very slowly. The impression of the 

 whorls in the matrix presents a faint lineation, too regular to be due to lines of 

 growth merely. The aperture is oblique and semilunar, but is too imperfect to enable 

 me to say whether the peristome was or was not thickened or reflected. On the 

 outer lip of the penultimate whorl are two linear impressions similar to those produced 

 by lamelliform teeth, to the presence of which they may, perhaps, be attributed ; but 



