132 
thicken the shell in some living examples, in fact one such is 
before me ; but the extent to which this extra-secretion of lime 
proceeds is not often met with in recent specimens of P. bivaricosus. 
The most marked differences, however, between the latter and var\ 
solidus lie in the peristome, where the outer and inner lips broaden, 
exposing repeated lamime of growth, the callosity on the body whorl 
thickens greatly, supporting strong tubercles and emarginations, 
whilst a roughening of the surface occurs on the outer, almost 
amounting to an immature denticulation, and the posterior 
angle of the peristome becomes much more acute, and is deeply 
channeled. Great variability is also noticed in the state of the 
umbilicus, this aperture in some cases becoming completely closed 
and overlapped by the spreading lamime of the pillar lip. 
The similarity of the var. solidus with some New Caledonian 
recent and fossil species, and a sub-fossil form from the Loyalty 
Islands is very marked, and demonstrates the fact that it must 
be regarded as a link between P. bivaricosus , on the one hand, 
and such species as P. ealedoniens, Petit, and P. j porphyrostomns , 
Pfeiffer, on the other. In both the latter the entire peristome 
is similarly thickened, the outer lip has a marked emargination 
or channel on the inner margin, more especially in P. ccdedonicus , 
whilst the pillar lip exhibits in both, an equally well marked, if 
smaller, callosity, and what is not visible in var. solidus , a deep 
emargination. Lastly, the twisting of the pillar lip seen in both 
the New Caledonian species is also faintly marked in some speci- 
mens of var. solidus from Lord Howe Island. Similar features 
are also traceable in the allied species P. cilex cinder, Crosse, and 
P. souvillei , Morelet. There is, however, one marked difference 
between all these shells and P. bivaricosus, var, solidus, the much 
rounder anterior margin of the peristome, and absence of the 
channel so characteristic of the posterior. 
Another ally of our species is P . bovinus, Brug.,* from New 
Zealand, more particularly in the modified presence of this an- 
terior channel, and in the irregular inner margin of the outer lip, 
which it will be remembered was above dwelt on as a character 
as the Lord Howe Island fossil. 
Mr. H. Crosse has proposed! a triple sub-division of the auricu- 
liform mouthed Bulimi. The first section is Placo stylus, as 
typified by B, fibratus , Martyn, B. ccdedonicus, B. alexander, B. 
souvillei , &c., in which the peristome is thick, the pillar lip 
(columella) twisted, and the callosity of the body whorl supporting 
a tubercle. The second section is Placostyli without a tubercle 
on the callosity, and a plain columella, typified by P. bovinus 
from New Zealand, and P. bivaricosus of Lord Howe Island, <fcc. 
* = P. shongii. Lesson. 
+ “ Etude critique aur les Bulimus auriculiforme s de la Nouvelle Calc- 
dome et dee Torres voisines,” Journ . ConchyL 1861, XII., p. 107. 
