HELTCODONTA. 287 



Risso, it has no claim for adoption, and had better be dropped en- 

 tirely. 



Key to Sections of Helicodonta. 



a. Spire deeply sunken, narrower than umbilicus ; aperture narrow- 

 crescentic, lip simple and retracted above, expanded and lipped 

 outwardly and below. Nautilus-shaped, Drepanostoma. 



aa. Spire wide, nearly level or convex. 



6. Aperture triangular or square, lip teeth 2 or obsolete, pe- 

 riphery rounded. 



c. Not ribbed; last whorl wider than preceding; spire 



nearly level, Helicodonta s. s. 



cc. Small, ribbed above, last whorl narrow as preceding ; 



spire convex, Aspasita. 



bb. Aperture lunate or rhombic; shell much depressed. 



c. Outer edge of parietal callus raised into an erect bar- 

 rier, Trissexodon. 

 cc. Parietal callus thin, wholly adnate, Caracollina. 

 bbb. Aperture lunate, toothless ; shell sub-globose, Klikia. 



Species. 



DREPANOSTOMA Porro. Nautiloid, biconcave, with crescentic 

 mouth. 



H. nautiliformis Porro., iii, 114. Lombardy. 

 drepanostoma Bk. 



HELICODONTA (Fer.) Risso. Species of middle Europe. 



H. angigyra Zgl. Rm., iii, 115. H. obvoluta. "' //J ^ 



stentzii Partsch /. pallida M.-T. 



H. obvoluta Mull., iii, 115. v. bosniaca Bttg., iii, 115. 



trigonophora Lam. v. blanci Poll., viii, 150. 



bilabiata Oliv. H. holoserica Stud., iii, 116. 



holosericea Gmel. diodontostoma Bgt. 



/. dentata Held. v. pluridentata Poll., iii, 116. 



/. edentata West. H. diodonta Miihlf., iii, 116. 



Chinese species of Helicodonta. 



H. subobvolutaAnc. J. B.,xi,308. H. diplomphala Moll., iii, 124. 

 H. molina Hde. H. uninodata Gred.,viii, 150. 



H. biconcava Hde., iii, 117. H. binodata Mlldff., iii, 124. 



outangensis Crosse. ? bicallosula Hde. 



