THE CYOLOPHO'RID LAND MOLLUiSfKS OF AMERHCIA 215 



simple, both the outer and inner lips somewhat thickened. The pari- 

 etal wall is covered by a heavy callus, which renders the peristome com- 

 plete. There is a slight impressed line between this callus and the 

 preceding turn. Operculum typically neocyclotid. 



Tlie type, U.S.N.M. No. 524005, comes from Polvon, Nicaragua. It 

 has 4.7 whorls and measures : Height, 16.5 mm. ; greater diameter, 21.1 

 mm. ; lesser diameter, 15.1 mm. Height of aperture, 10.8 mm. ; diame- 

 ter, 10.6 mm. 



U.S.N.M. No. 4087T9 contains 17 topotypes. U.S.N.M. No. 36863 

 contains 20 specimens collected by Dr. Flint in Nicaragua. U.S.N.M. 

 No. 347613, 1 specimen from Dirio, Nicaragua. 



The following four lots came from Nicaragua without specific local- 

 ity : U.S.N.M. No. 43478, 3 specimens ; U.S.N.M. No. 21729, 1 specimen ; 

 U.S.N.M. No. 57770, 3 specimens ; and U.S.N.M. No. 11249, 2 specimens. 



This subspecies, while related to A. {N.) dysoni valerioi, can readily 

 be distinguished from it by not having the base bicolor. 



APEROSTOMA (NEOCYCLOTUS) DYSONI COOKEI, new subspecies 



Plate 29, Figures 10-12 



Shell rather small, helicoid. The first whorl pale flesh colored; 

 all but the last of the succeeding turns rose-red ; the latter bright olive 

 or pale chestnut-brown. The nucleus consists of 2 small, well-rounded, 

 smooth turns. The postnuclear whorls are strongly rounded. The 

 penultimate turn is marked by wavy axial riblets, which are not quite 

 so wide as the spaces that separate them. On the last whorl these 

 riblets become more wavy, slightly vermiculated, and less strongly 

 developed, becoming evanescent on the last portion of the turn. Suture 

 rather strongly impressed. Periphery well rounded. Base narrowly 

 umbilicated, inflated, marked by the same sculpture found on the upper 

 surface of the last whorl, except on the umbilical wall, which shows 

 feeble riblike incremental lines. Aperture subcircular, with an angu- 

 lation at the posterior angle, somewhat effuse at the junction of the 

 basal and outer lip ; peristome simple, the outer thin ; the inner slightly 

 thickened and a little more curved than the outer. The parietal wall 

 with a moderately thick callus. Operculum typically neocyclotid. 



The type, U.S.N.M. No. 524006, was collected by C. Wythe Cooke, for 

 whom the species is named, at Uaxactun, Peten Province, Guatemala. 

 It has 4.3 whorls and measures : Height, 12.6 mm. ; greater diameter, 

 16.8 mm. ; lesser diameter, 12 mm. Height of aperture, 8.3 mm. ; diam- 

 eter, 8.2 mm. 



U.S.N.M. No. 382745 contains 140 topotypes representing various 

 stages of development which show great variation in size. The ex- 

 tremes are represented by the following figures : The smallest has 3.7 



