66 STREPTAXTS. 



S. ARGENTINA, Strobel. PI. 13, figs. 58-60. Magn. ^. 



Widely umbilicated, orbicularly depressed, almost discoidal, 

 diaphanous, shining, whitish, fragile ; whorls 5, flattened, thinly 

 striated, slowly increasing, suture deep ; lip expanded. 



Diam. 6 mill. 



Mendoza and Bahia Blanca, Argentine Republic. 



Unfigured and Undetermined Species of the Ammonoceras group. 



S. SEMPERI, Doring. Argentine Republic. 



S. SPIRORBIS, Deshayes. Near Rio Janeiro, Brazil. 



S. NITIDULTJS and S. AMAZONICUS, Dohrn. 



Province of Para, Brazil. 



S. MUTATA, Gould. Brazil. 



Gould remarks in his u Otia," that this may = insignis, Orb., 

 w r hich also resembles a Streptaxis. The species is not included 

 in the " Mollusca of the Wilkes Expedition." 



S. PROBLEMATIC^, Pfr. PL 12, fig. 15. India. 



S. BOMBAX, Benson. PI. 12, figs. 26, 27. India. 



These two species are both probably juvenile shells of 

 Eu streptaxis. 



Section DISCARTEMON, Pfeiffer. 



> 



S. DISCUS, Pfeiffer. PL 16, figs. 77-79. 



Smooth, irregularly varicose ; whorls 6^, flattened above, with 

 a slightly prominent apex ; the last whorl deflected near the 

 aperture ; aperture subhorizontal, transversely auriform, with an 

 oblique parietal plica ; lip reflected, the upper margin impressed 

 and obsoletely dentate, the outer margin with a stronger tooth, 

 the base transversely callous; hyaline white. Diam., 14 mill. 



Hob. unknown. 

 S. CRYPTODON, Moricand. PL 16, figs. 87-89. 



Smoothish and somewhat solid, pellucid, greenish white; 

 whorls 5 ; umbilicus moderate, cylindrical ; aperture scarcely 

 oblique, depressed lunar, tridentate, one conical parietal tooth, 

 and two obtuse ones on the basal margin, perisiome somewhat 



callously thickened, simple. Diam., 5*5 mill. 



Brazil. 



