16 STREPTAXID®. 
STREPTAXIS, Gray, 1837. 
Syn.—Artemon, Beck, 1837. 
Distr.—i5 sp. Mostly South American; Africa; East Indies. 
Shell oval, heliciform but often oblique, profoundly umbili- 
cated; whorls rapidly enlarging, deviating from the original 
axis more or less; aperture lunar, with or without teeth; lip 
slightly thickened and reflected. 
The principal character of the group is found in the singular 
oblique spiral of the whorls causing a torsion of the axis of 
revolution. 
ARTEMON, Pfeiffer, 1855. (Hpistylia, Pfr., 1877.) Aperture 
without teeth; shell subregular. American. 8S. candidus, Spix. 
scoLopoNTA, Déring. Shellsimilar to that of Hyalina. Front 
part of the animal elongated ; teeth of the radula dagger-shaped, 
the median very short, rhombic. S. Semveri, Diring. Argen- 
tine Republic. 
AMMONOCERAS, Pfeiffer, 1855. Shell depressed orbicular, 
shining, pellucid, thin, radiately striate; umbiiicus wide, per- 
spective; spire rather flattened; last whorl not descending at 
the aperture, the periphery rounded; aperture large, rounded 
lunate ; lip simple, acute, its extremities approaching. 8. omo- 
lomorpha, Orb. 
DISCARTEMON, Pfeiffer, 1855. Shell conoidal or discoidal; 
parietal wall and outer lip armed with teeth. S. discus, Pfr. 
EUSTREPTAXIS, Pfeiffer, 1877. Typical group. 8S. contusus, 
Fer. (xcii,55). S. comboides, d’Orb. (xcii, 56). S. deformis, Fer. 
(xen, 57): 
ODONTARTEMON, Pfeiffer, 1855. Shell ovate; parietal wall and 
outer lip armed with teeth. S. bulbulus, Morelet. 
OmpHALopTyx, Bottger, 1875. 
Distr.—Hesse. O. supracostata, Bottger. Fossil. 
Shell heliciform, subperforated, conical and costulated above, 
smooth below; last whorl very large, a little contracted at the 
aperture; aperture small, a little oblique, semilunar; outer lip 
simple, sharp; columella thickened at the base, reflected over 
the umbilical perforation; parietal wall with a horizontal plica- 
tion. Is supposed to be related to Streptaxis. 
EnneA, H. and A. Adams, 1855. 
Distr.—58 sp. Africa, Mauritius, Madagascar, India, ete. 
E. Liberiana, Lea (xcii, 58). Liberia. 
Shell subeylindrical, slightly rimate, apex obtuse, smooth, 
shining, hyaline; whorls flattened, the last narrow, sulcate 
externally in the middle, lamellate within, with a strong plait 
parallel to the columella; aperture subcircular; parietal lamella 
extending inwards and situated close to the right margin; 
