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 oil'-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 laminae 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 apertui'e in some cases becoming completely closed 

 and overlapped by the spreading laminas of the pillar lip. 



Tlie similarity of the var. solidiis with some Xew 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. hivaricosus, on the one hand, 

 and such species as P. caledoidcits, Petit, and P. porphyrostomus, 

 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. caledonicus, 

 whilst the pillar lip exhibits in both, an equally well marked, if 

 smaller, callosity, and what is not visil»le 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. ale.vaiuier, Crosse, and 

 P. souvillei, Morelet. There is, however, one marked ditlerence 

 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 proposedf a triple sub-division of the auricu- 

 liform mouthed Bulimi. The first section is Placostylus, as 

 typified by B. fibratus, Martyn, JJ. caledouicus, B. alexander, B. 

 souvillei, tfcc, 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, &c. 



* ^^ p. shomjii. Lesson. 



t " Etude criti<]ue aur les Bulimus anriculiformcs dc la Noiivelle C'alc- 

 donie et dee Terres voisiaes," Journ. Conchyl., 1801, Xll., p. 107. 



