CONCHOLOGY. 149 



FAMILY XVII. 



Alata. Three genera. 



1. Rostellaria. Three species. 

 Lamarck formed this genus from the Strombus of Lin- 

 nseus on account of having a sinus in the lower part of the 

 right margin contiguous to the canal. The beak is gener- 

 ally curved, and short in comparison to the length of the 

 spire, but sometimes it is straight, and equal in length to 

 the other part of the shell. 



The R. rectirostris is one of the most rare shells known. 

 Shell sub-depressed, turreted, with spire produced and 

 pointed ; aperture oval by the excavation of the columellar 

 edge ; the right margin dilating by age, and having a sinus 

 contiguous to the pointed canal which terminates the shell. 

 Rostellaria curvirostris. Rostellaria rectirostris. 



R. pes-Pelicani. 



R. curvirostris. The curved beak Rostellaria. PI. 27, 

 fig. 2. 



Species with the right edge digitated. 



R. pes-Pelicani. The Pelican's foot Rostellaria. 



Species turreted, with four digitations on the right edge ; 

 body and volutions ribbed longitudinally and crowned with 

 papillae ; flesh-coloured or white. 



2. Pteroceras. Seven species. 



Formed from the Strombus, being distinct from it by not 

 having the canal at the base shortened or truncated. It 

 greatly resembles the Rostellaria, but the sinus of the right 

 margin is distant from the body. From its digitation or 

 long recurved claws it has often been called the Spider 

 Shell. 



Shell oblong-ovate, ventricose, canal elongated, attenuated, 

 and often closed ; right margin dilating by age into an ex- 

 panded, digitated wing, attached to and covering a short 



