131 
The variety now about to be described was referred to in the 
following words : — “ This variation in the thickness is carried to 
the extreme condition in the sub-fossil examples of B. bivaricosus , 
in which the shell becomes thickened to an enormous extent, but in 
this case even gradations can be traced to the existing condition 
of the species. This variety 1 purpose calling B. bivaricosus , var 
solida .” 
Placostylus , Beck, is usually adopted by authors as a section* 
of Bulimulus , but I am quite in accord with othersf who use the 
term in a full generic sense. The characters of the lingual ribbon, 
are I think sufficient grounds for this, and that this portion of 
Bulimus bivaricosus , Gaskoin, supports such a view will be 
amply demonstrated by Mr. Charles Hedley in his descriptions of 
the Lord Howe Island land shells. 
Genus Placostylus, Beck. 
Placostylus bivaricosus, Gaskoin , sp. 
var. solidus, Eth. fil. 
(Plate xx., figs. 1-7.) 
Bulimus bivaricosus , Gaskoin, Proc. Zook Soe., 1854, XX., p. 152, 
t. 29, f. 4 and 5. 
Bulimus bivaricosus , var. solida , Eth. fil., Mem. Austr. Mus., 
No. 2, 1889, p. 27. 
Var. Char . — Shell larger than the species proper, thick, and to 
some extent rugged from the roughness of the oblique semi-imbri- 
cating sculpture, which irregularly crenulates the edges of the 
sutures. Spire relatively longer, and to some extent more acute; 
sutures at times somewhat channeled ; last whorl more inflated. 
Peristome enormously thickened, the callosity extending between 
the outer and pillar lips across the body of the whorl in a very 
marked manner, exposing many concentric laminae of growth, the 
outer edge of such thickening often projecting likeavarex; inner 
edges of the lips sinuous and sometimes deeply emarginate, or 
channeled at the anterior and posterior ends of the peristome, 
the latter more or less sharply angled ; callosity of the pillar lip 
rising into tubercles, usually well pronounced, opposite the anterior 
emargination and posterior angle of the aperture, the posterior 
tubercle being the largest. 
Obs . — The above characters are, to a very much less extent, 
visible in some one or other of a large assemblage of the species 
proper, but in the var. solidus , all are of a very pronounced nature, 
so much so, that had these shells been met with in an older fossili- 
ferous formation, they would at once have been erected into a 
separate species. No doubt there is a tendency to occasionally 
* Fischer, Man. Conchyl. et de Pal. Conchyl., 1887, p. 474. 
f Hutton, Trans. N. Zealand Inst., 1881, xiv., p. 152. 
