162 BULLETIN 181, UlSriTEiD SITATEiS NIAITTO'ISIIAL MUSEfUM 



CALAPEROSTOMA PURUM (Forbes) 



Plate 20, FiGimES 20, 21 

 1850. Cyclostoma ptirum Foebes, Proc. Zool. Soc. London, 1850, p. 56, pi. 9, fig. 9. 



Shell orbicular, depressed, white, somewhat shining. The apex is 

 slightly reflected, yellowish. Whorls 6, rounded, spirally sulcate. 

 Sulci numerous, transversely striate. Aperture subcircular, oblique. 

 Peritreme simple. Umbilicus very broad. Operculum? 



Height, 17 mm. ; greater diameter, 48 mm. 



Forbes does not cite a locality with his description. In his intro- 

 duction he says that the specimens he described were obtained during 

 the surveying voyage of the Harald and Pandora, which covered 

 various points between the coast of Ecuador and Vancouver Island, 

 Galapagos, and Pitcairn Islands, and the Sandwich Islands. 



The character of the shell would mark it as a South American 

 species. 



Its large size and depressed form readily distinguish it from the 

 other members of the genus. 



We have seen no specimens of this species and give Forbes' descrip- 

 tion and reproduce his figure. 



CALAPEROSTOMA CHANCHAPOYASENSE (Da Costa) 



Plate 21, Figttkes 4-6 



1906. Amphicyclotus chanchapoyasensis Da Costa, Proc. Malac. Soc. London, 



vol. 7, p. 9, pi. 1, figs. 11-13. 

 1912. Amphicyclotus chanchopoyasensis Kobelt, Martini-Chemnitz Conchylien 



Cabinet, vol. 1, sect. 19, p. 916, pi. 134, figs. 16-18. 



Shell depressed-helicoid, covered with a wood-brown periostracum. 

 The spiral cords and the axial riblets at irregular distances are dark 

 brown, thus giving to the surface of the shell a somewhat fenestrated 

 appearance. The nucleus consists of about one smooth turn, which is 

 followed by whorls that show low rounded raised spiral threads, of 

 which 9 are present on the next to the last whorl and 12 between 

 the summit and the suture on the last whorl. In addition to these 

 spiral threads the whorls are marked by strong incremental lines, 

 which are almost riblike in places, as well as by finer lines of growth. 

 Suture strongly impressed, almost channeled. Periphery strongly 

 rounded. Base inflated, strongly rounded, and marked by 12 spiral 

 cords, which grow successively weaker from the periphery toward 

 the umbilicus. The umbilical wall shows very feeble spiral threads. 

 In addition to this the entire base and umbilical wall are marked by 

 axial sculpture resembing that of the spire. Base very broadly 

 openly umbilicated, showing all the whorls. Aperture oblique, cir- 

 cular, somewhat protracted at the posterior angle ; peristome simple. 

 Operculum with central nucleus having about 12 whorls, the upturned 



