HELICIDA. on 
dilated. Jaw oxygnathous. H. pellis-serpentis, Chemn. (xevi, 
93). 26 sp. South America. 
Psadara, Miller. Smaller and thinner, hairy, not keeled. 6 
sp. So. America. 
GonostoMA, Held, 1837. (Anchistoma, Kobelt, 1871.) Shell 
umbilicated, orbicularly depressed, with close volutions, often 
with fugacious hairs; whorls 5-7, slowly increasing, the last 
angulate or acutely carinate above; aperture oblique, narrowly 
lunar, often sinuate; peristome labiate, reflected, sometimes 
callous; parietal wall unarmed. Jaw odontognathous. 
Drepanostoma, Porro, 1836. Shell discoidal, planorbiform, 
the last whorl nearly covering the previous ones, so that the 
axis is concave above and below; profoundly umbilicated ; aper- 
ture subvertical; the outer lip reflected. H. nautiliformis, Porro 
(xeiv, 19, 20). Italy. ‘ 
Trigonostoma, Fitz., 1833. (Helicodonta, Risso, 1826. Vortex, 
Beck, 1837. Euphemia, Leach, 1846.) Typical group. H. holo- 
sericea, Studer (xciv, 21). 5 sp. Europe. 
Caracolina, Ehr., 1831. (Caracollina, Beck, 1837.) _H. len- 
ticula, Fer. (xciv, 22). 25 sp. Mediterranean region, Madeira, ete. 
Sculptaria, Pfeiffer,1855. Uncharacterized. H. sculpturata, 
Gray. 2sp. W. Africa. 
Ophiogyra, Albers, 1850. Shell discoidal, many-whorled, 
plane above, concave below, showing all the whorls on either 
side; aperture very oblique, rounded; peristome slightly reflected, 
its extremities connected by a parietal callus. 
Polygyratia, Gray, 1847. H. polygyrata, Born (xciv, 23). 
Brazil. 
Systrophia, Pfeiffer, 1855. 15 sp. Central and South America. 
Hi. helicycloides, Orb. 
CORILLA, Adams, 1855. (Atopa [part], Albers.) Often sinis- 
tral, widely umbilicated, discoidal, plane above, convex at base ; 
last whorl compressed at the side, anteriorly deflected ; peristome 
thickened, reflected, the margins joined by an elevated callns 
emitting a strong re-entering lamina. H. Rivolii, Desh. (xciv, 
24). 8sp. India, ete. 
Stegodera, Martens, 1876. Shell like Corilla, but without 
parietal plica. H. angusticollis, Martens. China. 
Ptectopylis, Benson, 1860. Shell usually sinistral, subdiscoidal, 
widely umbilicated; parietal wall with a horizontal plica or 
ridge; several ridges within the aperture at irregular intervals, 
the first of them more or less remote. H. letophis, Benson (xciv, 
25). 24 sp. India, Burmah. 
#oista, Albers, 1850. Shell widely and profoundly umbili- 
cated ; spire depressed conic; whorls slowly enlarging, the last 
well rounded; aperture small, oblique, subcircular; peristome 
