HELTCID^. 33 



dilated. Jaw oxygnathous. H. 2^6llis-serpe,ntis, Chemn. (xcvi, 

 98). 26 sp. South America. 



Psadara, Miller. Smaller and thinner, hairy, not keeled. 6 

 sp. So. America. 



GONOSTOMA, Held, 1831. (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. 



Drepanostovia^ 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 

 (xciv, 19, 20). Italy. 



T7'igo7iostoma,¥itz.,1833. (Helicodonta, Risso, 1826. Vortex, 

 Beck, 1837. Euphemia, Leach, 1846.) Tjq^ical group. H. holo- 

 sericea, Studer (xciv, 21). 5 sp. Europe. 



Caracolina, Ehr., 1831. (Caracollina, Beck, 1837.) H. len- 

 ticula, F er. (xciy, 22). 25 sp. Mediterranean region, Madeira, etc. 



Sculptaria, Ffe[ffer,lS55. Uncharacterized. H.sculpturata^ 

 Gray. 2 sp. W. Africa. 



Ophiogyra, Albers, 1850. Shell discoidal, many-Avhorled, 

 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. j^olygyrata, Born (xciv, 23). 

 Brazil. 



Systrophia, Pfeiff'er, 1855. 15 sp. Central and South America. 

 H. helicycloides, Orb. 



GORILLA, Adams, 1855. (Atopa [part], Albers.) Often sinis- 

 tral, widely umbilicated, discoidal, plane above, convex at base ; 

 last whorl compressed at the side, anteriorl}^ deflected ; peristome 

 thickened, reflected, the margins joined by an elevated callus 

 emitting a strong re-entering lamina. M. Bivolii, Desh. (xciv, 

 24). 8 sp. India, etc. 



Stegodera^ Martens, 1876. Shell like Gorilla, but without 

 parietal plica. H. angusticollis, Martens. China. 



Ftectopylis, 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. leiophis^ Benson (xciv, 

 25). 24 sp. India, Burmah. 



^GiSTA, Albers, 1850. Shell widely and pi-ofoundly umbili- 

 cated ; spire depressed conic ; whorls slowly enlarging, the last 

 well rounded ; aperture small, oblique, subcircular ; peristome 



