76 



very conspicuous tooth which becomes developed at the lower portion of the 

 lip ; the distinction is not, however, universally admitted, as several of the 

 Purpura exhibit indications of a tooth, and the animals of the two genera, 

 are identical. 



1. acuminatum, Sow. 



2. brevidens, Conrad. 



3. calcar, Desk. 



4. cingulatum, Lam. 



5. crassilabrum, Lam. 



Species 



6. cymatum (fine), Sol. 11. maculatum, Gray. 



7. giganteum, Less. 



8. glabratum, Lam. 



9. grande, Gray. 

 10. imbricatum, Lam. 



12. punctatum, Gray. 



13. truncatum, Reeve. 

 11. tuberculatum, Gray. 

 15. unicarinatum, Sow. 



Figure. 



Monocekos grande. Plate 6. Fig. 29. Shell, showing the aperture and 

 prominent tooth. 



Genus 19. PURPURA, Lamarck. 



Animal; disc large, slightly acuminated in front, acuminately 

 rounded behind, carrying at the extremity a thin horny semi- 

 lunar operculum ; head rather small and fattened, prolonged at 

 each extremity into two pedunculated tentacles, at the summit of 

 the thickened portion of which, extending to one half or two 

 thirds of the length, are the eyes ; respiratory siphon of mode- 

 rate length ; proboscis small. 



Shell; ovate, or oblong-ovate, generally noduled or tuberculated, 

 spire short ; last tohorl swollen, more or less widely inflated, 

 with the aperture dilated and mostly grooved ; base emarginated ; 

 columella more or less depressly flattened ; lip generally denti- 

 culated. 



The terms Krfpvg, Murex, and Hopcpvpa, Purpura, were used indiscrimately 

 by ancient Greek writers in reference to all mollusks yielding a purple 

 juice, and they became objects of especial interest in that remote age, 

 on account of the limited sources then known of obtaining colour. Who 

 has not heard of the purple dye, produced by the ' Tyrius murex ' of Ovid, 

 (Murex trunculus Linn.), which no doubt abounded on the shores of the 

 ancient Phoenician city of Tyros. 



The purple juice of the mollusk affords, however, no assistance to the 

 systematist ; it abounds alike in animals of very dissimilar character ; in 



