176 HYPSELOSTOMA. 



pressed spire. The animal therefore carries the shell in- 

 verted. In other species the aperture approaches more to the 

 vertical position, though it always looks upward somewhat. 



The genus Tonkinia of Mabille has not been described or 

 illustrated well enough to permit one to form a definite 

 opinion, but for the present it may be placed in the synonymy 

 of Hypsclostoma. It was defined as follows : 



Shell discoidal with convex spire ; last whorl strongly cari- 

 iiate, inverted at the end, carrying a toothed aperture, pro- 

 vided with a sinus or oval gutter at the summit and towards 

 the suture ; umbilicus wide, permitting the whorls to be seen 



(MaUlle}. 



The few continental species known belong to several 

 groups. H. annamiticiim appears to be somewhat related to 

 Philippine species. I do not know where H. laidlawi belongs, 

 and the same is true of H. dayanum, which lias been placed 

 in Paraboysidia. 



The single Loochooaii species is closely related to those of 

 the Philippines. 



The Philippine group consists of species having spiral stria- 

 tion (sometimes present only on early whorls), a thin peri- 

 stome, and there is usually no basal plica. It may be regarded 

 as a natural group, of common ancestry ; but the modifications 

 have been considerable, two extremes being represented by 

 H. edentulum, in which the aperture is slightly oblique and 

 toothless, and H. roebeleni, having the shell depressed and the 

 aperture turned up, as in H. t \i~bifcrum. I have not seen H. 

 polijodon or H. pusillum. It is likely that many more species 

 will be found, as those known are scattered from Luzon to 

 Bohol, many intervening islands having none recorded. 



H. laidlawi, no. 4, and H. dayanum (Boysidiaf dayana) are 

 not included in the following 



Key to Species of Hypsclostoma. 



a. Diameter about double the altitude, openly umbilicate, 

 with low-conoid or depressed spire, the aperture turned 

 upward, nearly horizontal. 



