HORN EXPEDITION—MOLLUSCA. 
197 
Localities .—This is one of the few species of the genus which extends through¬ 
out the Larapiiitine area, having been collected in its southern part at Ilpilla 
Gorge and in the ravines about Illainurta, in the north-west in the gorge of the 
Darwent River, in the north in the gorges of the Upper Finke and its tributaries, 
Finke River Gorge, the ravines about Stuart’s Pass, at Painta Sjiring, Alice 
Springs, and Maude River in Hart Range, in more central localities at Tenipe 
Downs (type J. Thornton)., Glen of Palms, and Palm Creek. 
Variation .— T. adcockiana proves to be an exceedingly variable species, and 
various attempts on my part to deliniinate subordinate groups have failed. The 
variations can therefore be treated only in the following general terms :— 
1st. Sculpture .—In the type this consists of arched subacute growth-ridges, 
rather crowded, being wider than the interspaces, hardly conspicuous to the 
unaided eye, excepting at the suture. This condition passes to an extreme form, 
wherein the ribs are elevated, less numerous, and as wide or narrower than the 
interspaces. 
2nd. Colour {a ).—The epidermis is usually well-developed and of a yellowish- 
horn colour, that of the underside yellow or greenish-yellow ; but the type-form is 
devoid of a periostracum, or it is so thin and pellucid as not to conceal the opaque- 
white ground-colour of the test, {b) Colour-bands.—The. type shows two rufous 
bands on the body-whorl, one sutural, the other peripheral. In addition to these 
there is more frequently than not a broad infra-peripheral infuscation. This 
colouration belongs chiefly to the coarsely sculptured individuals. Whilst some 
of them have two bands only, some individuals of the finely-sculptured sort have a 
third colour-band. 
3rd. Shape .—The variation in shape is chiefly in the amount of the elevation 
of the spire, but more or less co-ordinate therewith is a variation in the outline of 
the aperture and the width of the umbilicus. 
A planulate specimen with fine sculpture measures 12 by 6‘25, that is, the 
proportion of the major diameter to the height is 100 to 52 ; the type, as well as 
others with coarse sculpture, the proportion is 100 to 70 ; an intermediate stage, 
not infrequent, measures 100 to 59, whilst an extreme in the opposite direction 
has the proportion 100 to 74. 
In the planulate forms the lips of the aperture approximate much nearer, and 
the aperture is consequently oboval insbjad of elliptic-oval. 
