54 Lamarck's Genera of Shells. 



3d Family. 

 Purpuritera. (11 Genera.) 



Shell with a short posteriorly ascending canal, or oblique notch 

 or semi-canal at the base of the aperture, inclining towards the 

 back. 



The canal at the base of the aperture is almost lost in the shells 

 of this family, most of them having merely an oblique notch, in- 

 clining backwards, and very perceptible when we examine the 

 hinder part of the shell. They all appear to have opercula. 



Lamarck has called this family purpurifera, because the trache- 

 lipoda which produce the shells it comprehends, especially those 

 of the genus purpura, secrete, in a particular reservoir, the colour- 

 ing matter from which the Romans formed their celebrated purple 

 dye, the use of which has been superseded by the discovery of the 

 cochineal. 



The genera are separated into two subdivisions. 1. Those with 

 the canal ascending, or curved towards the back. 2. Those with 

 an oblique notch, inclining backwards. The former subdivision 

 contains two, the latter nine genera. 



1st Subdivision. 



Canal ascending, or curved towards the back. 



1. Cassidaria*. 



Shell subovate, or oblong oval. Aperture longitudinal, narrow, 



terminated at the base by a curved subascending canal. Right lip 



varicose, or folded back ; left lip covering the columella, generally 



rough, granular, tubercular, or wrinkled. 



Distinguished from cassis by being, in general, less inflated than 

 that shell, but chiefly by the short canal, which terminates the 

 lower part of the aperture, not being abruptly turned towards the 

 back of the shell, and by its also being only slightly curved, or 

 ascending. 



The spire of the cassidaria is short, conoidal, with convex whorls, 

 and without any continuous varices. The left lip rests on the 



* As allied to the Cassis. 



