PLICAXIS. 13 



whorls smooth, apex obtuse ; whorls numerous ( 10-13 in 

 known species) . Aperture irregularly pirif orrn, the columella 

 excavated below, prominent at its junction with the parietal 

 wall. Soft anatomy unknown. 



Type P. mirabilis. Distribution, Perak, Malay Peninsula. 



No definition of this group has been published by Mr. 

 Sykes, but its special character seems to be the presence of a 

 prominence on the axial border, invading the aperture. In 

 P. mirabilis the columella seems to be slightly twisted, and the 

 parietal wall bulges above it; in P. perakensis the columella 

 seems to describe a wide spiral gyration. Otherwise the shell 

 is like Prosopeas. The two species seem from the published 

 figures to differ in columellar structure, and that they be- 

 long together is not at all certain. 



1. P. MIRABILIS (Sykes). PI. 4, figs. 1, 2. 



1 ' Shell recalling in form Rhodina perakensis de Morgan, but 

 the earlier whorls increase more rapidly, and the lower half 

 of the shell has a more cylindrical appearance. The colu- 

 mella is twisted, and a revolving keel encircles the base and 

 ascends spirally into the shell, about half way up the colu- 

 mella wall ; in addition, another keel is visible from the junc- 

 tion of the suture line and the outer lip until, revolving 

 round the periphery, it fades out where it bisects the outer 

 lip. Whorls 13, earlier ones smooth, later ones strongly 

 striate. Alt. 24.5, diam. max. 3.5 mm." (Sykes). 



Malay Peninsula: Kelantan (J. Waterstradt) . 



Rhodina (?) mirabilis SYKES, Journal of Malacology, ix, 

 1902, p. 22; t. c., p. 61, pi. 3, f. 2; x, p. 1. 



This species is the type of the genus Plicaxis, though Mr. 

 Sykes did not actually use the combination Plicaxis mirabilis. 



2. P. PERAKENSIS (de Morgan). PI. 4, figs. 3, 4, 5. 



Shell cylindric, subulate, fragile, brown, corneous, com- 

 posed of 10 regularly convoluted whorls ; stria? of growth very 

 well marked and irregular; suture linear and very strongly 

 impressed. Aperture triangular, oblique, at an angle of 

 about 30 degrees with the axis of the shell ; peristome straight 



