OF MOLLUSCA. 151 



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

 pletely covered with a callous deposit ; inner edge of whorls 

 simple. 



•f 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. caerulescens. Photinula c, Adams, Gen. Moll. t. 48. f. 9 a, 



operculum. 



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



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 $• Hanley, B. M. t. D.D. f. 1 . 



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



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



4. G.?? 1, 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. leevis. 



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, 



