GASTROPODA 555 



Key to the families of Rachiglossa here described: 



di Shell rough, with ridges, tubercles, or spines. 



&i Central teeth without cusps 2. COLUMBELLIDAE 



6 a Central teeth with cusps. 



c x Laterals without cusps 1. MURICIDAE 



c a Laterals with 2 or 3 cusps. 



d t Centrals with many cusps 3. NASSIDAE 



d a Centrals with 5 to 7 cusps 4. BUCCINIDAE 



d 3 Centrals with 2 cusps 5. TUBBINELLIDAE 



o a Shell smooth and polished. 



&! Shell with a tall spire 6. MITBIDAE 



6, Shell with a low spire 7. OLIVIDAK 



FAMILY 1. MURICIDAE. 



Shell thick and solid, with an elevated spire with a rough surface 

 on which are usually rows of protuberances or spines; siphonal canal 

 often long; eyes sessile, at the outer base of 

 the tentacles; central tooth of radula with 

 at least 3 long cusps (Fig. 870, 1) ; laterals 

 without any: about 15 genera and 1,000 spe- 

 cies, which are mostly tropical; they feed 

 largely on other mollusks, the shells of which ^ 870 _ Radula of Murex 

 they are able to pierce with the radula in the ( * 1 ^ n ^?2$tS& 

 proboscis. 



Key to the genera of Muriddae here described : 



0^ Whorls angular, with distinct protuberances or spines. 



6 X Spines and protuberances usually very prominent 1. MUREX 



Z> 2 About 10 longitudinal ridges : 3. EUPLEUBA 



a? Whorls rounded. 



&! Longitudinal ridges very distinct 2. UBOSALPINX 



1), Revolving ridges very distinct 4. PURPURA 



1. MUREX L. Spiny rock-shell. Shell thick, ovate or elongated; 

 spire prominent; 3 or more rows of prominent protuberances or spines; 

 aperture round, ending below in a long canal: about 300 species, in 

 tropical and temperate seas. It was largely from M. trunculus L. and 

 M, brandaris L. that the well known Tyrean or imperial purple dye of 

 the ancients was obtained, a large mucous gland in the mantle furnishing 

 a yellowish secretion which turns purple on exposure to the light. The 

 secretion was obtained by crushing the animals, and large heaps of the 

 broken shells of these two species may now be found where ancient manu- 

 factories of the dye existed, M. trunculus being found principally on the 

 Syrian coast and M. brandaris in Greece and Italy. 



M. festivus Hinds. Length 5 cm.; width 2.5 cm.; color white; 

 canal closed: Californian coast, towards the south. 



