208 BULLETIQSr ISl, UlSriTED SrriATES NIATIOINIAIL MUSEUM 



1858. Cyclotus dysoni Pfeiffer, Monographia pneumonopomorum viventium, 



vol. 2, p. 19. 

 1860. Platy stoma (Aperostoma) dysoni Morch, Malak. Blatter, vol. 7, p. 66, 

 1888. Neocyclotus dysoni Fischee and Ceosse, Mission scientifique au Mexique 



et dans TAm^rique centrale, vol. 2, pt. 7, p. 164, in part. 

 1890. Cyclotus (Aperostoma) dysoni von Martens, Biologia Centrali-Americana, 



p. 3, in part. 

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



Michigan, No. 137, p. 33. 



Shell rather large, helicoid, covered by an olivaceous straw-colored 

 periostracum, in which the last whorl has an orange tinge. The 

 anterior half of the base has a paler coloration than the posterior 

 half, which gives this a bicolor aspect; interior of the aperture 

 bluish white. When denuded the shell is soiled white. The nucleus 

 consists of 2 small, well-rounded, smooth turns. The postnuclear 

 whorls are well rounded; the last one has an impressed groove a 

 little below the summit, which is upturned and appressed to the 

 preceding turn almost forming a cord. The postnuclear whorls are 

 marked by rather coarse, vermiculated, slightly retractively slanting 

 riblets, which are about as wide as the spaces that separate them. 

 Suture well marked. Periphery well rounded. Base openly um- 

 bilicated, inflated, well rounded, and marked by the continuation 

 of the sculpture that characterizes the upper surface of the last 

 whorl, except the umbilical wall, which is marked only by riblike 

 incremental lines. Aperture circular, except the slightly drawn-out 

 angle at the posterior angle ; peristome simple, that of the outer lip 

 thin; the inner somewhat thickened. The parietal wall is covered 

 by a thick callus, which continues the columellar lip to the posterior 

 angle. There is a deep impressed line behind the parietal callus, 

 which is slightly Innately incised. The operculum is typically 

 neocyclotid. 



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

 321029, received from Sowerby and Fulton and labeled "Honduras." 

 It has 4.5 whorls and measures : Height, 18.7 mm. ; greater diameter, 

 25.9 mm.; lesser diameter, 18 mm. Height of aperture, 13 mm.; 

 diameter, 13 mm. 



U.S.N.M. No. 316388 contains two specimens received from Cum- 

 ing from Honduras; U.S.N.M. No. 321025, three specimens collected 

 by C. T. Simpson in Spanish Honduras. 



This subspecies most closely resembles A. (N.) dysoni aurernn. 

 Like aureum, it does not have the axial riblets fine or closely spaced, 

 and like it it has the whorls somewhat flattened toward the summit, 

 but it is easily distinguished from aureum by its much larger size, 

 exceeding 25 mm. in greater diameter, while aureum has less than 

 20 mm. 



