18 HELICOIDEA. 



GONOSPiRA, Swainson, 1840. (Gibbulina, Pfr., 1855.) Typical 

 group. G^. joaZan^a, Fer. (xcii, 65). Isle of France. 



NEVILLIA, Martens. Whorls narrow, with strong perpendicular 

 ribs. 3 sp. Mauritius. G. clavulata^ Lam, 



E.AVENIA, Crosse, 18Y3. 



Distr. — B. Blandi, Crosse fxcii, 66). Cura9ao. 



Shell allied to Spiraxis and Pupa, turreted, imperforate, sub- 

 hyaline, columellar margin spirally twisted, outer margin bent 

 inwards, and with a strong tooth in the middle. 



Family HELICOIDEA. 



Shell heliciform, with usually depressed conical spire, and 

 umbilicated ; outer lip simple. 



Animal differing from the ti'ue Helices by the absence of a jaw. 



Rhytida, Albers, 1860. 



Disti\ — 31 sp. Australia, Tasmania, New Caledonia, etc. R. 

 bullacea, Pfr. (xcii, 67). Australia. 



Shell umbilicate, thin, convexly depressed ; undulately rugose 

 or striate ; spire slightly elevated ; whorls four or five, slightly 

 flattened ; umbilicus wide and deep ; aperture oblong-ovate, 

 sometimes dentate within ; lip simple, acute, its extremities 

 approaching. 



Viviparous. Teeth rather few, obliqu^e, arcuated. 



DiPLOMPHALUS, Crossc and Fischer, 1873. Shell discoidal, 

 planorbiform, spire depressed ; peristome simple, connected by 

 a much-developed parietal callus. 13 species. New Caledonia, 

 New Zealand, Australia. D. Megei, Lamb, (xeiii, 68, 69). N. Cale- 

 donia. Differs from Rhytida b}^ the very wide umbilicus and 

 sunken excavation of the upper face of the shell ; in the radula 

 by the equal size of the lateral teeth. 



GuESTiERiA, Crosse, 1872. 



Distr. — G. Powisiana, Pfr. New Grenada. 



Shell imperforate, corneou.s, thin, depressed, quite involute, 

 the last whorl only visible ; aperture like that of Nautilus; peris- 

 tome thin, simple. Animal unknown. 



Aerope, Albers, 1860. 



Distr. — A. caffra, Fer. So. Africa. 



Shell very thin, subglobose, costulately striate, with narrow 

 umbilicus ; spire not prominent, obtuse ; whorls four, ventricose, 

 strongly striated, the last descending at the aperture ; aperture 

 large, semiovate ; lip simple, acute ; columellar margin widelj- 

 reflected. 



Teeth verjr long, subulate, arranged in converging lines. 



