414 TROCHINiE. 



The genus Tectus has the appearance of being umbi- 

 licated, but, in reality, the axis is imperforate ; the shells 

 are at once recognised by the short, spiral twist formed by 

 the fore part of the columella, and which serves to cha- 

 racterize the genus. 



Species of Tectus. 



architectonicus, A. Adams. ForskiUii, Bolt. 



caperatus, Phil. leucogaster, A. Adams. 



crenulatus, Lam. Mauritianus, Gmel. 



dentatus, Forsk. pyramis, Born. 



fenestratus, Gmel. prasinus, Mke. 



ferruginosus, Phil. triserialis, Lam. 



Genus POLYDONTA, Schumacher. 



Shell conoidal, axis imperforate ; whorls almost always 

 granulated, the last angulated ; aperture nearly rhom- 

 boidal; columella spirally twisted, forming a funnel- 

 shaped, false umbilicus, the margin furnished anteriorly 

 with many teeth. 



Syn. Lamprostoma, Swains., not Rajin. 



Ex. P. Sandwichensis, Eydoux, pi. 47, fig. 2. Oper- 

 culum, P. lineata, Lamarck, fig. 2, a. Shell, P. lineata, 

 fig. 2, b. 



The front, sharp, free edge of the columella in Polydonta 

 is armed with numerous teeth, and does not end in a sim- 

 ple point, as in Tectus ; the genus is distinguished from 

 Clanculus by the conoidal shape and simple outer lip of 

 the shell. 



Species of Polydonta. 



aspera, Chem. concinna, Phil. 



callicoccus, Phil. conspersa, Gmel. 



