PLACOSTYLUS, LORD HOWE ISLAND. 27 



Bulimus ^JBurytus) etheridgei BRAZIER, Australian Mus. Mem., 

 no. 2, 1889, explanation to pi. 5 (name only), pi. 5, f. 1, 2, 7, 8 

 (figures reversed). Placostylus bivaricosus var. Etheridgei Braz., 

 HEDLEY, t. c., p. 141. 



A thin, obliquely ovate form. 



Var. SOLIDUS (Etheridge). PL 12, figs. 6, 7, 8. 



Shell larger than the species proper, thick, and to some extent 

 rugged from the roughness of the oblique semi-imbricating sculpture 

 which irregularly crenulates the edges of the sutures. Spire rela- 

 tively longer, jmd to some extent more acute ; sutures at times some- 

 what channeled ; last whorl more inflated. Peristome enormously 

 thickened ; the callosity extending between the outer and the pillar 

 lips across the body of the whorl in a very marked manner, exposing 

 many concentric laminae of growth ; the outer edge of such thick- 

 ening often projecting like a varix ; 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 -emargi nation and posterior angle 

 of the aperture, the posterior tubercle being the largest. (Etheridge.) 



Coral rock and overlying calcareous sand dunes, Lord Howe Island. 



J3. bivaricosus var. solida ETHERIDGE, Austr. Mus. Mem. no. 2, 

 p. 27 (1889). Placostylus bivaricosus var. solidus ETH., Rec. Austr. 

 Mus. i, no. 7, p. 131, pi. 20, f. 1-6. 



Fig. 2 of pi. 12 is a recent specimen approaching the var. solidus, 

 the typical form of which occurs only fossil, though in a very recent, 

 probably pleistocene deposit. 



Mr. Etheridge further observes as follow? : 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 fossiliferous formation, they would at once 

 have been erected into a separate species. No doubt there is a 

 tendency to occasionally thicken the shell in some living examples, in 

 fact, one such is before me ; but the extent to which this extra secre- 

 tion 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 



