THE CTCILOPHORID LAND MOLLUSCES OF AMEKIOA 243 



cated, inflated, strongly rounded and marked by the continuation of 

 the axial ribs which grow much stronger on the umbilical wall. Aper- 

 ture very large, circular, with an angulation at the posterior angle; 

 peristome simple; the outer lip thin, slightly effuse at the junction 

 of the basal and outer lip; a little thickened on the inner lip. The 

 parietal wall is covered by a thick callus, which renders the peritreme 

 complete. 



The type, U.S.N.M. No. 307425, was received from Sowerby and 

 Fulton with the label "Brazil." It has 4.3 whorls and measures: 

 Height, 17.3 mm.; greater diameter, 29.9 mm.; lesser diameter, 21.5 

 mm. Height of aperture, 12 mm. ; diameter, 13.4 mm. 



This species agrees with A. (A.) amazonense in having the base 

 strongly axially ribbed but differs from it in having a much larger 

 aperture. 



APEROSTOMA (APEROSTOMA) AMAZONENSE, new species 



PiATE 35, Figures 4-6 



Shell decidedly depressed-helicoid, almost planorbid. The entire 

 upper surface is covered by a pale chestnut-brown periostracum. 

 There is a faint lighter zone immediately above the periphery. The 

 base is bicolor. The posterior half is a little darker than the upper 

 surface of the shell, while the anterior half and umbilical wall are 

 much lighter; interior of aperture bluish white. The nucleus con- 

 sists of 2 small, well-rounded, smooth turns; the postnuclear whorls 

 are moderately rounded, the last one deflected for a quarter of a turn. 

 The postnuclear whorls are marked by retractively curved axial rib- 

 lets, which are not quite as wide as the spaces that separate them. 

 These riblets become decidedly enfeebled on the last portion of the 

 last turn. Suture strongly impressed. Periphery weakly angulated. 

 Base broadly umbilicated, inflated, strongly rounded and marked by 

 strong axial ribs, which are more pronounced on the umbilical wall 

 than on the rest. Aperture subcircular, slightly angulated at the pos- 

 terior angle; peristome simple; the outer and inner lips both some- 

 what thickened and slightly reflected. The parietal wall is covered by 

 a thick callus which renders the peritreme complete. The operculum 

 is typically aperostomid and shows about 10 whorls. 



The type, U.S.N.M. No. 356102, was collected by E. H. Short on 

 the Amazon River in Brazil. It has 4.5 whorls and measures: 

 Height, 13 mm. ; greater diameter, 24 mm. ; lesser diameter, 18.1 mm. 

 Height of aperture, 9 mm. ; diameter, 9.9 mm. 



There are two additional lots, both bearing merely the label "Bra- 

 zil"; U.S.N.M. No. 307425 contains one specimen and U.S.N.M. 

 No. 316236, three specimens. 



