242 
GASTEROPODA OF THE INFERIOR OOLITE. 
179. PsEUDOMELAEiA COARCTATA, DeslofigcJiamps, 1842. Plate XVIII, figs. 9 a, 9 b, 
9 c, and varieties Plate 
XIX, figs. 1 a, 1 b. 
1842. Melania coaectata, Deslong champs. Mem. Soc. Linn. Norm., vol. vii, 
p. 226, pi. xii, figs. 11 and 12. 
1842. — TUEEis, Deslong champs. Vol. cit., p. 224, pi. xii, fig. 8. 
1852. Chemnitzia coaectata, d'Orbigny. Terr. Jur., ii, p. 45, pi. ccxl, figs. 1, 
2,3. 
Bibliography, ^c. — Irrespective of their gorgeous colouring Deslongchamps’ 
figures of this fine species seem to give a better idea of its form than those of 
d’Orbigny, though it is generally admitted that there is no necessity for main- 
taining a distinction between Melania coarctata and Melania turris. In Dorsetshire 
there is no difficulty in dealing with the species, but further north the specimens 
are found in worse condition, and the evidences are less clear. 
Description : 
Spiral angle .... 18° — 20°. 
Height of whorl to width . . . 1 : 1'45. 
Length .... 70 — 100 mm. 
Shell strongly turrited in the adult whorls, but having the subapical whorls 
without any salience. The young form can scarcely be distinguished from 
Ps. lineata ; there is a difference in the colour-bands of individual specimens, but 
no evidence that this is a constant feature. But specimens such as fig. 9 c already 
begin to show a sudden increase of the body-whorls. After this stage is reached 
the sudden increase of the whorls is maintained throughout, but differs consider- 
ably in degree. The posterior portion of each whorl is provided with a bevilled 
edge terminating in a carina, below which there is a constriction of the whorls ; 
the anterior portion of the whorl is without any raised edge. Elexuous colour- 
bands, more or less parallel to the axis, are seen in some specimens, and appear 
to be more characteristic of Ps. coarctata than of any other species. Specimens 
from the Gadomensis-hedi, Oborne, show this feature well, as also the fine cross- 
hatcliing produced by spiral lineation decussating with the fine lines of growth. 
Varieties . — PI. XIX, fig. 1 a, represents a specimen from the Humphriesianus- 
zone at Oborne, where a slight rise is observable in the anterior portion of the 
whorl, whilst the posterior keel is less prominent, and the sutural sulcus better 
defined. This is a variety of Ps. coarctata, slightly in the direction of Ps. Lons- 
dalei, Morris and Lycett. 
