THE CYOLOPHORID LAND MOLLUSKS OF AMEiBICA 211 



measures : Height, 18.7 mm. ; greater diameter, 25.8 mm. ; lesser diam- 

 eter, 17.7 mm. Height of aperture, 12 mm. ; diameter, 13 mm. 



This subspecies resembles A. (N.) dysoni sumichrasti but is larger, 

 with a thinner, less effuse columellar lip and a more effuse outer 

 lip. The posterior angle of the aperture also is less strongly produced. 



APEROSTOMA (NEOCYCLOTUS) DYSONI AMBIGUUM (von Martens) 



PiATE 28, Figures 10-12 



1890. Cijclotus (Aperostomu) dysoni amUguus von Mabtens, Biologia Centrali- 



Americana, p. 4. 

 1897. Neocyclotus (Neocyclotus) dysoni ambiguus Kobelt and Moixendobef, 



Nachrb. deutschen malak. Ges., vol. 29, p. 137. 

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



Univ. Michigan, No. 137, p. 34. 



Shell moderately large, helicoid, covered with an olivaceous straw- 

 colored periostracum. The nucleus consists of 2 well-rounded, smooth 

 turns. The postnuclear whorls are inflated, strongly, evenly rounded, 

 not flattened at the summit. The riblets on the penultimate whorl 

 are straight and retractively curved; on the last whorl, the last half 

 of which is very short, rough, and coarse, the axial sculpture assumes 

 a vermiculated form separated by spaces a little wider than the ribs. 

 Suture rendered strongly impressed by the slightly inbent summit 

 of the turns. Periphery well rounded. Base quite narrowly umbili- 

 cated, strongly inflated and rounded. The posterior half is marked 

 like the upper surface of the last turn; the anterior half is marked 

 by very rough, riblike, flattened incremental elements. Aperture 

 subcircular, slightly protracted at the posterior angle; peristome 

 simple, the outer lip thin, the inner lip a little expanded and a little 

 reflected near the umbilicus. The parietal wall is covered by a mod- 

 rately thick callus. Operculum typically neocyclotid. 



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

 56966, collected by the Mexican Geographical Commission at Jalapa, 

 Veracruz, Mexico. It has 4.3 whorls and measures: Height, 16.7 

 mm. ; greater diameter, 22.9 mm. ; lesser diameter, 16.3 mm. Height 

 of aperture, 11 mm. ; diameter, 11.5 mm. 



Three additional lots are in the collection of the National Museum : 

 No. 58314, one specimen from Actopan, Veracruz, collected by the 

 Mexican Geographical Commission; the other two lots are labeled 

 "Mexico," without specific locality. One of these, No. 321009, con- 

 tains one specimen collected by Salle; the other. No. 321026, con- 

 tains two specimens from the Redfield collection. 



This subspecies recalls A. {N.) dysoni berendti (Pfeiffer) but can 

 readily be differentiated by its larger size and the absence of spiral 

 markings. 



