HYGROMIA, AULACOSPIRA. 279 



H. bideus Chemn., iii, 170. H. bicallosa Friv., iii, 171. 



bidentata Gin. 

 v. diodon Parr., iii, 171. 

 dibothrion Friv. 



Section Metodontia Mollendorff, 1886. 



Metodontia MLLDFF., Jahrb. D. M. Ges., 1886, p. 191, type H. 

 hemipleuris. Tetrodontina ANCEY, Conch. Exch. i, p. 64, May, 

 1887. See HILBER, Sitzungsber. k. Akad. Wissensch., Ixxxvi, pi. 



I, f. 1-3, development of aperture armature. 



Shell perforate, globose-turbinate or subdepressed, brown or 

 whitish ; whorls numerous and narrow, the last not descending in 

 front. Aperture lunate, nearly closed by two large lip teeth usually 

 situated on a ridge of callus, opposed to two smaller teeth on the 

 parietal wall. Lip thin-edged, expanded below, reflexed at colu- 

 mellar insertion. Type H. hemipleuris Mlldff. 



Anatomy unknown. The group seems most nearly allied to 

 Dibothrion of the Eur.-Asian fauna. It has nothing to do with the 

 American group Triodopsis. 



The group is confined to the dry northern half of China, being 

 about coextensive with the Loss formation. 



H. hemipleuris Moll., iii, 149. H. houaiensis Cr., iii, 149. 



moltneri Gredl. obstructa Hde. not Fer. 



H. yantaiensis C. & D., iii, 149. 

 v. tetrodon Moll., iii, 149. 



Genus AULACOSPIRA Mollendorff, 1890. 



Aulacospira MLLDFF., Bericht tiber die Senckenbergische natur- 

 forschende Gesellschaft in Frankfurt a. M., 1890, p. 224. Micro- 

 petasus MLLDFF., I. c. 



Shell small, umbilicate, of thin corneous structure; uuicolored, 

 pale brown. Spire more or less raised, from the beginning sub- 

 scalar and keeled ; whorls 4 to 5, striatulate, flattened or with spiral 

 concavity, the last whorl keeled or rounded. Aperture oblique, 

 generally subcircular, with to 5 teeth a short distance within ; 

 peristome thin, reflexed. Type A. scalatella Mlldff., pi. 64, figs. 10, 



II, 12. 



