228 BTJLLETESr 181, UlSnTEiD STDATEiS N1ATT0IN1AIL MUSEUM 



are marked by regular, almost vertical, slender riblets, which are 

 separated by spaces no wider than the riblets. On the succeeding 

 turns the axial riblets become reduced to incremental lines, and on 

 the last one in addition to these oblique, irregularly scattered, im- 

 pressed scratches are present, which cause the spaces between them 

 to appear as basal rugosities. Periphery feebly angulated. Base 

 inflated, strongly rounded, broadly openly umbilicated, and marked 

 like the spire. The umbilical wall is marked by incremental lines. 

 Aperture large, subcircular, slightly auriculated at the posterior 

 angle; peristome simple, thin all around. 



The specimen described and figured, U.S.N.M. No. 116667, comes 

 from the Lea collection and bears no locality label. It has 4.4 whorls 

 and measures: Height, 12 mm.; greater diameter, 15.9 mm.; lesser 

 diameter, 12.5 mm. 



The small size readily distinguishes this from all the other 

 Aperostomas. 



APEROSTOMA (APEROSTOMA) CINGULATUM (Sowerby) 

 PlATE 31, FIGUBES 22-24 



1843. Cyclostoma dngulatum Sowbxby, Thesaurus conchyliorum, vol. 1, p. 93, 



pi. 29, figs. 213-214. 

 1852. Cyclotus cingnlatus Pfeiffeb, Monographia pneumonopomorum viventium, 



vol. 1, p. 18. 

 1866. Cyclotus angulatus Bland, Amer. Journ. Conch., vol. 2, p. 59 (error for 



cingulatus; not angulatus von Martens 1874). 

 1897. Neocydotus (Neocyclotus) cimgulatus Kobex,t and Moulendobff, Nachrb. 



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

 1923. Poteria (Neocyclotus) dngulatum H. B. Bakeb, Occ. Pap. Mus. Zool. 



Univ. Michigan, No. 137, p. 42. 



Shell depressed-helicoid, covered with a very dark chestnut-brown 

 periostracum ; the early denuded whorls reddish. The nucleus con- 

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

 are well rounded, the last slightly flattened below the suture. The 

 first postnuclear whorl is marked by slender, retractively curved, 

 somewhat irregular, fine, rather closely spaced riblets, which become 

 very much enfeebled on the last half of the last turn and toward 

 the end completely lost. In adition to this, the upper surface of 

 the last whorl is irregularly slightly malleated. Suture well im- 

 pressed. Periphery very feebly angulated. Base moderately broadly 

 openly umbilicated, inflated, and marked by rather irregular wavy 

 axial riblets, which become very much intensified on the umbilical 

 wall, and rather conspicuous malleations stronger than those on the 

 upper surface. Aperture oblique, circular, slightly angulated at the 

 posterior angle ; peristome simple, thin on the outer lip and thickened 

 on the inner, with a very heavy callus on the parietal wall, which 



