Description of a Libyan Desert land shell
Abstract
Exiliberus jacksoni, novo gen. et sp. Mr. H. A. Longman, Director of the Queensland Museum, has forwarded a very interesting land shell for description. Five specimens were received from Corporal Kenneth Jackson, of the Queensland Museum staff, on active service in Libya, with the following note:
"Species of land snail from the Libyan Desert Plateau, Western Egypt. These animals are scattered amongst the limestone rocks and protect themselves by secreting a substance which forms a membrane inside the shell opening. Before sandstorms they anchor themselves to the rocks with the same secretion. What do they live on? I found this strange species in one isolated spot only."
The shells are comparatively large, globosely lenticular, upper and lower surfaces roundly convex, the periphery with a sharp pinched keel. Coloration cream. Whorls 4 1/2, the first smooth, the succeeding ones coarsely sculptured. The earlier whorls are flattened, the antepenultimate more rounded, and the last descending towards the aperture half the depth of the whorl. The sculpture consists of very irregular radial closely packed ridges, crossed with a few faint concentric lines somewhat more notable on the last whorl, but sometimes these may become obsolete. Apparently due to their anchoring as noted above, new outer lips are formed curiously sandgrained, and these persist as browner, rougher ridges for a full quarter of a whorl, descending more steeply, with the number reaching thirty or more ridges. The undersurface is convex and sculptured similarly to the upper surface. The mouth is subcircular, the outer lip thickened but not reflected, the columella short, slanting, and thickly spread over the umbilical area, a thick glaze connecting with the outer lip. The measurements of the type are: Breadth, 46 mm.; height, 32 mm.; breadth of aperture, 22 mm.; height of aperture, 19 mm.
No Egyptian snail similar has been traced here in literature, and the figure given by Thiele in the Handbuch, p. 719, fig. 761, of Iberus gualterianus shows its general appearance. As the shell characters differ from those of Eremina and its associates in northern Africa, the strong keeling, sculpture and form being distinctive, the species is named jacksoni after its discoverer, and the genus Exiliberus introduced for its reception. This name is given to record the similarity to Iberus, but not as an indication of its close .affinity, as the likeness may be due to convergence only.
