206 BULLETIN 181, UNITED STtATES NIATIOINAIL MUSEUM 



APEROSTOMA (NEOCYCLOTUS) DYSONI HINKLEYI, new sabspecies 

 Plate 28, Figtjees 19-21 



Shell rather large, helicoid, covered with a brownish-olivaceous 

 periostracum. The anterior two-fifths of the base and umbilical wall, 

 however, is paler than the rest of the base, and this gives to the base 

 a bicolor effect. When denuded all the whorls are soiled flesh colored ; 

 interior of aperture bluish white. The nucleus consists of a little 

 more than 2 small, well-rounded, smooth turns. The postnuclear 

 whorls are well rounded except at the suture, where on the last whorl 

 there is a decided groove a little below the summit ; the summit itself 

 is again elevated and appressed to the preceding turn. The postnu- 

 clear whorls are marked by strong, retractively curved, anastomosing, 

 irregularly wavy riblets, which are as wide as the spaces that separate 

 them. These riblets are rather fine compared with most of the mem- 

 bers of the genus, and closely spaced. Suture well impressed. Periph- 

 ery well rounded. Base inflated, strongly rounded, openly umbili- 

 cated, the width of the umbilicus being about one-fifth of the diameter 

 of the shell. The base is marked by the continuation of the sculpture, 

 which characterizes the upper surface of the last turn. The umbilical 

 wall, however, has only riblike incremental elements, which extend 

 upon the base slightly beyond the outer edge of the umbilicus. Aper- 

 ture almost circular, slightly drawn out at the junction of the outer 

 and basal lip and provided with a slender auricle at the posterior 

 angle ; peristome simple ; the outer lip sharp, the inner thickened and 

 somewhat reflected, extending up over the parietal wall almost un- 

 diminished to the posterior angle. The space between the peristome 

 of the parietal wall and the preceding whorl is an impressed groove, 

 which gives the impression of the last whorl being slightly solute. 

 This, however, is not the case, for the tip of the little auricle is ap- 

 pressed to the preceding turn. The parietal callus forms a concave 

 sinus as it slopes toward the columella. Operculum typically neo- 

 cyclotid. 



The type, U.S.N.M. No. 523968, was collected by F. Sarg in Guate- 

 mala. It has 4.4 whorls and measures: Height, 19.7 mm.; greater 

 diameter, 28.3 mm.; lesser diameter, 18.4 mm. Height of aperture, 

 14.2 mm. ; diameter, 14.6 mm. 



U.S.N.M. No. 32056 contains two topotypes. 



In addition to these there are eight lots in the collection of the 

 United States National Museum, all from Guatemala, as follows: 

 No. 426003, 2 specimens from Cacao Finca, Trece Aguas, near Senahu, 

 Alta Vera Paz; No. 365367, 1 specimen from Chama, Alta Vera Paz; 

 No. 365666, 2 specimens from Chama, Alta Vera Paz; No. 226026, 2 

 specimens from Cacao; No. 425985, 3 specimens from the vicinity of 

 Secanquim, Alta Vera Paz, at an altitude of 550 meters; No. 185498, 



