212 BULLETIOSr 181, UNITEiD STlATElS NiATTOdSIlAiL MUSEUM 



APEROSTOMA (NEOCYCLOTUS) DYSONI BERENDTI (Pfeiffer) 



Plate 29, Figures 4-6 



1861. Cyclotus (?) berendti Pfeiffer, Malak. Blatter, vol. 8, p. 171. 



1863. Cyclotus berendti Pfeiffer, Nov. Conch., vol. 2, p. 232, pi. 59, figs. 22-23. 



1886. Neocijclotus berendti Fischer and Crosse, Mission scientifique au Mexique 



et dans I'Amerique centrale, vol. 2, pt. 7, pi. 38, figs. 4-5. 

 1888. Neocyclotus berendti Fischer and Crosse, ibid., vol. 2, pt. 7, p. 167. 



1890. Cyclotus (Aperostoma) dysoni bereiidti voN Martens, Biologia Centrali- 



Americana, Moll., p. 5. 



1891. Cyclotus dysoni form multilineatus Pilsbrt, Proc. Acad. Nat. Sci. Phila- 



delphia, 1891, p. 325. 

 1923. Poteria (Neocyclotus) 'berendti H. B. Baker, Occ. Pap. Mus. Zool. Univ. 

 Michigan, No. 137, p. 33. 



Shell depressed, somewhat helicoid, covered with an olivaceous 

 straw-colored periostracum showing spiral white lines. The nucleus 

 consists of 2.2 small, rounded, smooth turns. The postnuclear whorls 

 are strongly rounded, appressed at the summit, and marked on the 

 penultimate whorl 'by straight, retraotively curved axial riblets, 

 which here are about as wide as the spaces that separate them. On 

 the last turn the axial sculpture becomes vermiculated with a re- 

 tractive slant. The axial sculpture is not strong. Suture rendered 

 strongly impressed by the inbent summit of the whorls. Periphery 

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

 with the axial sculpture characteristic of the upper surface of the 

 last turn, bending over the posterior half of the base, gradually fad- 

 ing toward its center. The anterior half and the umbilical wall 

 are marked by strong, riblike, incremental elements. Aperture sub- 

 circular, with a slight angulation at the posterior angle; outer lip 

 thin, effuse; the inner lip much less strongly curved than the outer 

 and somewhat thickened. The parietal wall is rendered complete 

 by the continuation of the peristome from the columella to the pos- 

 terior angle. This renders the last whorl slightly solute; in some 

 specimens decidedly so. The parietal callus is ovally incised. Oper- 

 culum typically neocyclotid. 



The specimen described and figured is one of 10, U.S.N.M. No. 

 251715, collected by Nelson and Goldman at Chichen Itza, Yucatan. 

 It has 4.3 whorls and measures : Height, 13.5 mm. ; greater diameter, 

 19.6 mm.; lesser diameter, 14 mm. Height of aperture, 8.3 mm.; 

 diameter, 9.2 mm. 



U.S.N.M. No. 467450 contains four additional specimens from the 

 same locality, while U.S.N.M. No. 424551 contains 45 specimens 

 in various stages of growth from the same locality collected by Mr. 

 and Mrs. Walter M. Gilbert, U.S.N.M. No. 162495 contains one speci- 

 men received from H. von Ihering labeled "Yucatan"; U.S.N.M. 



