THE CYCI^OPHORID LAISTD MOLLUSKS OF AMEIRJIOA 181 



MEXCYCLOTUS LUTESCENS (Pfeiffer) 



Plate 24, Figuees 13-15 



1851. Cyclostoma (Cyclophorus) lutescens Pfeiffee, Proc. Zool. Soc. London, 



1851, p. 250. 

 1854. Cyclostoma lutescens Pfeiffer, Martini-Chemnitz Conchylien Cabinet, 



vol. 1, sect. 19, p. 333, pi. 43, figs. 12-14. 

 1886. Eabropoma lutescens Fischer and Crosse, Mission scientifique au Mexique 



et dans I'Anierique centrale, vol. 2, pt. 7, pi. 38, fig. 2. 

 1888. Amphicyclotus lutescens Fischer and Crosse, ibid., vol. 2, pt. 7, p. 139. 

 1890. Cyclophorus (Amphicyclotus) lutescens von Martens, Biologia Centrali- 

 Americana, p. 6. 



1897. Cyrtotoma lutescens Kobelt and Mollendorff, Nachrb. deutschen malalc. 



Ges., vol. 29, p. 140. 



1898. Amphicyclotus lutescens Kobext and Mollendorff, Nachrb. deutschen 



malak. Ges., vol. 29, p. 139 (reprint). 

 1928. Aperostoma lutescens H. B. Baker, Oec. Pap. Mus. Zool., Univ. Michigan, 

 No. 193, p. 53. 



Shell depressed-helicoicl, covered with a straw-colored, orange- 

 tinged periostraciim, with the early whorls a little darker than the 

 later. Interior of the aperture bluish white. The nucleus consists of 

 one rounded smooth turn. The early postnuclear whorls are strongly 

 rounded and marked by rather distantly spaced, slender axial riblets 

 which become less regular and more closely spaced on the last whorl. 

 Suture strongly impressed. Periphery well rounded. Base well 

 rounded and marked by the weak continuation of the axial sculpture, 

 which extends over the umbilical wall. Umbilicus about one-fifth the 

 diameter of the shell. Aperture circular, slightly oblique ; peristome 

 slightly oblique, slightly protracted into an angle at the posterior 

 angle ; outer lip of the peristome thin ; the inner somewhat thickened. 



The specimen described and figured is one of two, U.S.N.M. No. 

 301012, collected by Salle in Mexico without specific locality. It has 

 4.6 whorls and measures : Height, 10.7 mm. ; greater diameter, 14.7 

 mm. ; lesser diameter, 11.8 mm. 



There are two additional lots, three specimens, in the collection of 

 the National Museum, without specific locality. 



This species can readily be distinguished from M. cooperi (Try on) 

 by its depressed form. 



MEGACYCLOTUS, new genus 



Amphicyclotine shells of helicoid shape. The whorls are marked 

 by fine spiral lines and heavier, decidedly retractively curved, coarser 

 diagonal threads on spire and base ; absent on the wall of the broad 

 umbilicus. Peristome slightly expanded on the outer lip. Operculum 

 thin, corneous, with central nucleus, the outer edge of whose upturned 

 volutions are rendered ragged by wear. They are retractively 

 striate. 



