274 BULLETIN 181, UNITED STATES NATEOINIAL MUSEfUM 



Suture strongly impressed. Periphery well rounded. Base moder- 

 ately openly umbilicated and marked by the continuation of the axial 

 sculpture, which here is a little stronger than on the spire. Aperture 

 subcircular, slightly protracted at the posterior angle; peristome 

 simple; outer lip thin; the inner slightly thickened. The parietal 

 wall is covered by a moderately thick callus which renders the peri- 

 treme complete. 



The type, Acad. Nat. Sci. Philadelphia No. 140876, was collected by 

 Euthven and Gaige in British Guiana. It has 4.3 whorls and meas- 

 ures: Height, 11.6 mm.; greater diameter, 15.5 mm.; lesser diameter, 

 11.2 mm. Height of aperture, 7.4 mm. ; diameter, 7.8 mm. 



In shape and in sculpture this subspecies most nearly resembles the 

 typical form, from which it can be differentiated readily by its much 

 smaller size. 



LIRACYCLOTUS, new genus 



Small aperostomine shells of helicoid shape, having the whorls 

 marked with low spiral threads. The operculum bears a low, re- 

 flected, calcareous spiral lamella, between whose turns the upturned 

 outer edge of the basal chondroid plate is apparent. 



Type: Liracyclotus psilomitus (Pfeiffer). 



Distribution : Venezuela. 



LreACYCLOTUS PSILOMITUS (Pfeiffer) 



Plate 19, Figures 7-9 



1851. Cyclostoma psilomitum Pfeiffeb, Proc. Zool. Soc. London, vol. 19, p. 250. 



1852. Cyclophorus psilomitus Pfeiffer, Monographia pneuinonopomorum viven- 



tium, vol. 1, p. 96. 

 1854. Cyclostoma psilomitum Pfeeffee. Martini-Chemnitz Conchylien Cabinet, 



vol. 1, sect. 19, p. 319, pi. 41, figs. 24-25. 

 1897. Amphicyclotus psilomitus Kobelt and Moixendobff, Nachrb. deutschen 



malak. Ges., vol. 29, p. 139. 



Shell small, helicoid, covered with a horn-colored periostracum. 

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

 clear whorls are strongly rounded and marked by slender spiral 

 threads of which 10 are present between the summit and periphery. 

 In addition, the whorls are marked by weak incremental lines and 

 numerous, heavy, unpressed axial resting stages, which render the 

 surface rather rough. The spiral threads are much narrower than 

 the spaces that separate them; they are not quite regularly spaced, 

 and there is a little broader zone with a spiral liration immediately 

 below the summit. Suture strongly impressed. Periphery well 

 rounded. Base moderately broadly umbilicated with rather strong, 

 low, rounded spiral threads, which are separated by mere impressed 

 lines. Of these, 14 are present between the periphery and the umbil- 



