J. S. Gardner — British Eocene Land-MoUusca. 243 



Fam. BuLiMiN^.^ 



BuLiMus (Amphidkomus) ellipticus,^ ^hy. sp. 1822. Plate VI. 



Figs. 3 and 4. 



The adult shell is sub -perforate ?, sinistral, oblong-ovate, bulimi- 

 form, composed of 8 whorls. 



The general form of the shell is that of a pupa, or chrysalis, the 

 penultimate whorl being almost of the same diameter as the body- 

 whorl. The apex is blunt. The whorls are at first more than twice 

 as wide as high, the fourth whorl in descending is in diameter twice 

 its height, the penultimate whorl in the specimen figured is 18 mm. 

 high against 31 mm. in diameter, and the body-whorl 42 mm. high, 

 with a diameter of 33 mm. All are irregularly tumid, bulging most 

 towards the lower suture. The test is thin. There are two varieties 

 of ribs, one coarse, with a millimetre interval between each, the 

 other fine, in which case 3 ribs occupy one millimetre ; the former 

 variety is the commoner, and, though I have not remarked both 

 occurring on the same individual, there are often very fine lines or 

 ribs in the intervals between the coarse ones. The suture is very 

 narrow, but defined. The aperture is ovate, sub-auricular, angular 

 above, its precise form being difficult to describe in words. The 

 peristome is continuous, thickened, and reflected, the columellar lip 

 being a little broader and united to the outer by a thickened callus. 

 The columella is slightly convoluted, and the columellar region 

 lightly excavated. The average length of the full-grown shell is 85 

 millimetres, or a little over 3^ inches, and this seems rarely if ever 

 to have been exceeded. 



The young are conical, with the last whorl subangular, shells of 

 2 centimetres in length having a spiral angle of about 55°, which 

 diminishes to about 45° when the length is doubled. The aperture 

 is semi-lunar or a little like an inverted comma, and the lips thin 

 and sharp. 



Casts of the young are very abundant in places, far more so than 

 of the adults. Associated with them in still greater abundance are 

 oviform bodies (Plate VI. Fig. 5), variable, but the great majority of 

 which are under 2^ to 3 centim. in length and to 16 mm. in diameter. 

 They are equal and rounded at both ends, with the sides flattened. 

 "When not merely casts, they are seen to be enveloped with a thin 

 calcareous shell of rugged texture. They are supposed to be eggs 

 or cocoons, and are sometimes hollow, or partly filled with arrago- 

 nite, but in general they are casts, with one end free, and the other 

 broken, and adhering to the matrix, as if the animal had effected its 

 escape. Several of the most promising have been slit for me, and 



1 That part of the genus to Avhich our fossils belong was separated into a genus 

 Coehlostyla, by Ferussac in 1819. The name, literally column-shells, indicates 

 sufficiently their general form. The true BiUinms has few whorls, the body -whorl 

 being very large and at least equalling in length all the rest of the spire. Amphi- 

 dromus is a smaller group or sub-genus of closely allied species usually sinistral. 

 These subdivisions seem useful in so enormous a genus. 



^ All the species, rmless otherwise stated, are described in F. E. Edwards' monograph 

 on the Eocene Mollusca, in the Paheontographical Society's volume for 1852, where the 

 bibliography of the species is detailed at length. Most of them are re-described iu 

 Sandberger's Land und Siisswasser Conchylien, "Wiesbaden, 1870-75. 



