224 
HORN EXPEDITION—MOLLUSCA. 
I’etractor muscle and finally enters a tube, which occupies the penis sac, but fi’om 
which, except at each end, it is free. This I interpret with some hesitation as an 
invaginated epiphallus, of which the distal end has grown to the atrium wall, and 
which has drawn after it into the penis sac both the vas deferens and the retractor 
muscle. No vestige of a flagellum is apparent. On opening the epiphallus, as 
in X. adcockiana (Fig. L.), two fleshy protuberances are seen near the entrance of 
the vas deferens, thence to the atrium the interior is ridged longitudinally by 
numerous corrugations. 
Whether this growth represents a degeneration from the Fpiphallagonous 
type (as I have here assumed) or an evolution of the Haplogonous model (in which 
case the tube of Xanthomelon might be the homologue of the pilaster of Polygyra) 
is a puzzle awaiting further data for solution. With reference to the latter it may 
l)e remarked that the penis of Dorcasia (Guide to Helices, Frontispiece, Fig. 3), 
in its lack of epiphallus and flagellum and in its mode of entry of the vas deferens 
outwardly resembles the arrangement of XaiifkameloH. To de.scend to lower lev^els 
of classification, the extraordinary character of the supposed introverted epiphallus, 
correlated with the remarkal)le and persistent feature of the shortness of the 
spermatheca duct, gives sufficient warrant for promoting Xanthomelon to full 
generic rardc. For, not only does it stand apart from Thersites with regard to 
these points, but it is also thereby distinguished from the supergeneric group of 
Thersites + ChJorith + Planispira + Papnina + Ganesella. My examination of 
X. pnchystyln, perinpiata^ adcockiana^ squamulosa^ granditnbercnlata^ and arcigerens 
induces me to unite to the typical members of Xanthomelon^ catalogued by Pilsbry, 
Guide to Helices, p. 135, both his “ group of hitieniataP p. 131, and the members 
of Angasella enumerated on p. 114. The attitude of Xanthomelon towards Rhagada 
and Glyptorhagada is beyond my knowledge. 
The territory now inhabited by Xanthomelon 'suggests that it spread from the 
Western Region, where, with Liparus, Succinea, Papa, etc., it formed the oldest 
surviving Australian snail-fauna. If, as seems improbable, it entered this 
continent, as Papnina and Chloritis certainly did, by way of Torres Straits, its 
arrival must have preceded theirs by a long interval of geological time. 
Xanthomelon adcockiana, Bednall. 
An examination of a single specimen from Palm Creek discovered a jaw 
(Fig. J) differing little from that of the preceding species. 
