OF MOLLUSCA. 155 



two external ribs ; inner edge with two crenated ribs ; axis umbili- 

 cated. Operculum horny, oblong, circular ; whorls five or six, rapidly 

 enlarging. — Adams, Gen. Moll. t. 25. f. 8 a, b. 



1. P. lutea. Solarium 1., Philippi, Moll. Sicil. i. 174; Adams, 

 Gen. Moll. t. 25. f. 8, shell and operculum only. 



" Animal exactly like Trochus." " Operculum very thin, of many 

 whorls, with a central calcareous nucleus on the inner side." — 

 Philippi, 



b. Shell subglobose ; aperture contracted ; whorls subcylindrical, 

 rounded in front . Monodontina. (Page 147.) 



f Pillar twisted, with a more or less distinct tooth in front. 



20. MONODONTA. 



Shell conic, ovate, solid, grooved and granulated ; axis imperforated 

 or covered ; aperture ovate ; pillar-lip with two strong opake tuber- 

 cles ; outer lip grooved ; throat pearly ; lateral beards 4*4. Oper- 

 culum with many gradually enlarging whorls. 



1. M.TOsilin, t. 43. f. 7, 8. 



2. M. tseniata, t. 63. f. 15, 17. 



3. M. canalifera, t. 64. f. 26, 29. 



21. Turcica. 



Shell conical, thin, granular ; axis imperforated ; aperture longer 

 than wide ; pillar thick, spirally twisted behind, blunt and prominent 

 in front; outer lip thin, simple. Operculum ? Animal ? 



1. T. monilifera, Adams, Gen. Moll. 423. t. 48. f. 3. 



22. Labio. 



Shell conical, ovate, solid, grooved, and often granulated; axis 

 perforated, at length covered ; aperture roundish ; pillar-lip thick, 

 rounded, with a slight prominence or tubercle in front. Operculum 

 horny, many-whorled. 



1. L. fragaroides, t. 42. f. 7- 



2 . L. ?, t. 108. f. 6. 



3. L. constrictus, t. 63. f. 23, 27. 



4. L. striolatus, t. 63. f. 18, 22. 



5. L. zelandicus, t. 64. f. 12, 15. 



6. L. cingulatus, t. 64. f. 16, 20. 



The lingual membrane and teeth of Labio crassus are like those of 

 Gibbula umbilicata. See figure of "Tongue," Osier, Phil. Trans. 

 1832, t. 14. f. 2. 



