OF MOLLUSCA. 151 



§§§§ Axis of shell perforated or umbilicated, more or less com- 

 pletely covered with a callous deposit ; inner edge of whorls 



j* Pillar-lip regularly arched. 



11. OXYSTELE. 



Shell top-shaped, solid, smooth ; axis perforated, covered with a 

 callous deposit ; aperture square ; pillar flattened, gradually blending 

 into the thin outer lip. 



1. O. merula, t. 42. f. 8. 



2. O. cserulescens. Photinula c, Adams, Gen. Moll. t. 48. f. 9 a, 



operculum. 



Some of the species of this genus are very like species of Labio. 



12. Trochiscus. 



Shell subdiscoidal, covered with a periostraca ; axis umbilicated, 

 open ; aperture nearly circular ; inner lip thin, flattened, rather pro- 

 duced in front, gradually blending into the outer lip. Operculum 

 horny, of many gradually enlarging whorls, with a thin, free, raised 

 external edge. 



1. T. Norrisii. 



Trochiscus is very nearly allied to Gibbula. Trochus oculus from 

 Australia appears to be the same in a semi-fossil state. 



13. Gibbula. 



Shell depressed, conical, solid ; axis perforated, more or less open ; 

 aperture subrhomboidal ; pillar arched gradually. Operculum of 

 many gradually enlarging whorls. 



* Axial cavity moderate. 



1. G. cineraria, t. 42. f. 5, 6 ; Forbes fy Hanley, B. M. t. D.D. f. 1. 



2. G. ?, t. 42. f. 9. 



3. G. ?, t. 42. f. 2. 



4. G.?? ?, t. 42. f. 4. 



5. G. ?, t. 42. f. 1. 



6. G. ?, t. 51. f. 1, 2. 



7. G. tumida. Trochus t., Forbes fy Hanley, B. M. t. D.D. f. 2. 



8. G. magus. Trochus m., Forbes fy Hanley, B. M. t. D.D. f. 3. 



** Axial cavity very wide. 



■ 9. G. pulligo. 

 10. G. lsevis. 



The species of this genus gradually pass into Omphalius. 



Central teeth of Gibbula magus broad, lanceolate ; apex lanceolate, 

 denticulated on each side ; four or five inner lateral linear-lanceolate, 



