186 BULLETEN 181, UlSriTEiD SIT'ATEiS NIATI'ONIAL MUSlEIimi 



Crosse and Fischer's specimen came from Tabasco Province, 

 Mexico, but we believe the specimen we have figured belongs here. 



The species is easily distinguished from the others by its small 

 size. 



AMPHICYCLOTUS TEXTURATUS (Sowerby) 



Plate 24, Figures 1-3 



1850. Cyelostoma texturatum So^'Krby, Thesaurus conchyliorum, Suppl., p. 160*, 



pi. 31A, fig. 303. 

 1852. Cyclopliorus texturattis Pfeiffer, Conspectus cyclostomaceorum emen- 



datus auctus . . ., p. 15. 

 1880. Aniphicijclotus texturatus Fischer and Crosse, Mission scientifique au 



Mexique et dans I'Am^rique centrale, vol. 2, pt. 7, pi. 35, figs. 2-2b. 

 1886. Amphicy clot lis textiiratus Fischer and Crosse, ibid., vol. 2, pt. 7, p. 144. 

 1890. CyclopJiorus (Amphicyclotus) texturatus von Martens, Biologia Centrali- 



Americana, p. 6. 



Shell depressed-helicoid, covered with a chestnut-brown peri- 

 ostracum. Nuclear whorls 1.5, small, well rounded, smooth. The 

 first postnuclear whorl is marked by fine incremental lines which are 

 more emphasized at the channeled suture and eventually developed 

 into little riblets before the real postnuclear sculpture is reached. 

 The later whorls are marked by strong vermiculations. Suture well 

 impressed. Periphery well rounded. Base openly umbilicated, with 

 the umbilicus about two-fifths of the diameter of the shell. The base 

 and umbilical wall are both marked by vermiculations, although on 

 the umbilical wall they become more elongated and more riblike. 

 Aperture circular, slightly angulated at the posterior angle; peri- 

 stome simple, thill. Parietal wall covered by a heavy callus. The 

 operculum has a subcentral nucleus and consists of about 10 whorls, 

 which are flattened and slightly free at the distal edge and striated. 



The specimen described and figured, U.S.N.M. No. 162491, comes 

 from Chiapas, Mexico. It has 5.5 whorls and measures : Height, 26.7 

 mm.; greater diameter, 41.1 mm.; lesser diameter, 29.7 mm. 



The collection of the National Museum contains additional 

 specimens as follows : 



U.S.N.M. No. 162310, from Coban, Guatemala; U.S.N.M. No. 

 200694, 1 from Finca Providencia, Guatemala ; U.S.N.M. No. 321044, 

 1 from Guatemala, without specific locality; U.S.N.M. No. 32072, 1 

 collected by F. Sarg in Guatemala; U.S.N.M. No. 316370, 2 from 

 Mexico, without specific locality. 



Subfamily Aperostominae Torre and Bartsch 

 This subfamily has been defined on p. 38. 



KEY TO THE MAINLAND GENERA OF THE SUBFAMILY APEROSTOMINAE 



Calcareous deposits on outside of vi'horls of operculum fused Aperostoma 



Calcareous deposits on outside of whorls of operculum not fused — Liracyclotus 



