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 I purpose calling £. bivaricosus, var 

 solida." 



PlacostyUis, Beck, is usually adopted by authors as a section* 

 of Bulinmdus, 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 tliat 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. Zool. Soc, 1854, XX., p. 152, 



t. 29, f. 4 and 5. 

 Bulimus bivaricosus, var. solida, Eth. fil., Mem. Austr. Mas., 

 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 like a varex ; 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 

 propel', 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. 

 t Hutton, Trans. N. Zealand Inst., 1881, xiv., p. 152. 



