OF MOLLUSCA. 143 



** Operculum with one or more spiral ribs. 



3. Marmorostoma. 

 Operculum with an indistinct subcentral rib, surrounded by a 

 broad flat margin. Shell turbinate, solid, deeply perforated ; spire 

 low ; aperture circular ; inner lip flattened and produced in front. 



1. M. undulatum, t. 38. f. 2, 3, t. 60. f. 9-14. 



2. M. versicolor, t. 38. f. 4, 6. 



4. Amyxa. 



Operculum with an indistinct, broad, subcentral rib, with a nar- 

 row, flat edge. Shell top-shaped, solid, imperforate ; aperture ovate ; 

 pillar-lip with a curved groove ; throat grooved. 



1. A. niger, 1. 108. f. 1. Prisogaster n., Adams, Gen. Moll. t. 43. f. 6. 



5. Modelia. 



Operculum with a convex, subcentral granular rib, and a sharp- 

 edged submarginal keel. Shell top-shaped, imperforated, thin, 

 granular ; spire conical ; aperture subcircular. 



1. M. granosus. Turbo g., Martyn. 



6. Callopoma. 



Operculum with a broad central and three or five submarginal 

 spiral ribs ; outer ribs toothed. Shell top-shaped, thick, imper- 

 forate ; spire conical ; aperture circular ; inner lip grooved, pro- 

 duced in front. 



1 . C. fluctuosum. Turbo fl., Gray. Opercular ribs five. 



2. C. saxosum. Turbo s., Gray. Opercular ribs three. 



7. NlNELLA. 



Operculum concave externally, and edged with two raised spiral 

 ribs and a thin edge. Shell top-shaped, depressed, rugose, deeply 

 umbilicated ; aperture circular, with an oblong concavity near the 

 pillar. 



1. N. lamellosa. Turbo 1., Brod. 



2. N. torquata, t. 39. f. 2. 



8. COLLONIA. 



Operculum circular, of many gradually enlarging whorls, with a 

 convex external rib and central pit. Shell top-shaped, solid, spirally 

 striated, imperforate ; aperture circular, contracted ; inner lip rather 

 callous. 



1. C. marginata. Delphinula m., Lamk. 



2. C. striata, Gray. Shell red, white-marbled, striated. Africa. 



