66 STREPTAXIS. 



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



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 Blanco, , Argentine Republic. 



Unfigured and Undetermined Species of the Ammonoceras group. 



S. SEMPERI, Doring. Argentine Republic. 



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



S. NITIDULUS and S. AMAZONICUS, Dohrn. 



Province of Para, Brazil. 



S. MUTATA, Gould. Brazil. 



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

 which 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 

 Eustreptaxis. 



Section DISCARTEMON, Pfeiffer. 



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



Smooth, irregularly varicose ; whorls 6J, 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. PI. 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, peristome somewhat 

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



Brazil. 



