THE CYiCJLOPHO'RID LAND MOLLUS'KS OF AMERICA 209 



APEROSTOMA (NEOCYCLOTUS) DYSONI AUREUM, new subspecies 



Plate 28, Figures 13-15 



1886. Neocyclotus dysoni Fischer and Cbosse (part), Mission scientifique au 

 mexique et dans I'Am^rique centrale, vol. 2, pt. 7, pi. 39, fig. 10. 



Shell small, helicoid, covered with a golden straw-colored periostra- 

 cum. When denuded, soiled white ; interior of aperture bluish white. 

 The nucleus consists of almost 2 small, well-rounded, smooth turns. 

 The postnuclear whorls are strongly rounded, slightly flattened below 

 the suture on the last whorl and marked by decidedly retractively 

 curved vermiculations, which are rather distantly spaced. Suture 

 strongly impressed. Periphery well rounded. Base narrowly openly 

 umbilicated, inflated, strongly rounded, and marked by the continua- 

 tion of the same type of sculpture as that characterizing the upper 

 surface of the last whorl, except the umbilical wall, which is marked 

 by riblike incremental lines only. Aperture rather small, almost cir- 

 cular, slightly angulated at the posterior angle ; peristome thin on the 

 outer lip, somewhat thickened on the inner lip, with a strong callus cov- 

 ering the parietal wall, which is slightly emarginate. Operculum typ- 

 ically neocyclotid. 



The type, U.S.N.M. No. 523970, comes from Panistlahuaca, Oaxaca, 

 Mexico. It has 4.2 whorls and measures: Height, 14.2 mm.; greater 

 diameter, 18.6 mm. ; lesser diameter, 13.7 mm. Height of aperture, 8.7 

 mm. ; diameter, 9.4 mm. 



U.S.N.M. No. 320656 contains three topotypes. 



This subspecies resembles ^. (N.) dysoni dysoni (Pfeiffer) in having 

 the vermiculations not fine or closely spaced but is easily distinguished 

 from it by its coloration and by being much smaller. The greater di- 

 ameter is less than 20 mm., while in dysoni it is more than 25 mm. 



APEROSTOMA (NEOCYCLOTUS) DYSONI SUMICHRASTI, new subspecies 



Plate 28, Figtjees 25-27 



Shell helicoid. Nuclear whorls eroded in all our specimens. Post- 

 nuclear whorls strongly rounded, with a depressed slight groove a lit- 

 tle anterior to the summit of the last whorl. The summit itself is ap- 

 pressed to the preceding turn. The whorls are marked by retractively 

 slanting anastomosing axial riblets, which are rather strong and sepa- 

 rated by spaces a little wider than the riblets. Suture well impressed. 

 Periphery well rounded. Base narrowly, openly umbilicated, inflated, 

 strongly rounded and marked like the upper surface of the last whorl, 

 except the umbilical wall, which is marked by strong riblike incremen- 

 tal elements. Aperture large, subcircular, with a rather conspicuous 

 angulation at the posterior angle, which bears a slight groove in the 

 middle ; peristome simple, outer lip thin ; the inner thickened and very 



