PURPURA. ir)9 



Tribulub. Spire depressed, whorls simple, the last ventricose ; aperture 

 wide ; columella arcuated ; inner lij) excavated, corrugated at the fore- 

 part. 



Thalessa. Sjjire elevated, whorls spinose, angulated at the upper iiart ; 

 aperture moderate ; columella rounded, tubercular in front ; outer lip 

 nodulous internally. 



Stramonita. Spire elevated, whorls simple or nodulous ; aperture 

 moderate, produced anteriorly ; columella rounded, simple in front. 



Trochia. Whorls separated by a deep groove ; inner lip thickened, 

 convex, striated ; aperture with a very short canal. 



PoLYTROPA. Spire acuminate, whorls foliated or tuberculose ; inner Up 

 flattened ; canal small, oblique ; aperture narrowed at the forepart. 



Cronia. Shell ovate ; spire acuminated ; aperture moderate ; inner lip 

 callous at the upper part ; columella straight, simple anteriorly. 



A^ Genus PURPURA, Brug. 



For tlio dentition of P. patula, L., see PI. 42, fig. l. The 

 same plate contains figures of the lingual armature of represen- 

 tatives of the dirterent subgeneric groups. 



The animal does not ditfer essentiall}' from that of Mnrex in 

 its general external and anatomical characters. The eyes are 

 usually placed near the tips of the tentacles, the siplion is sliort, 

 and the foot not large. 



About forty tertiary species have been described. 



P. PATULA, Linn. PI. 43, figs. 19-22. 



Brown, the ribs and nodules darker; the mucli excavated 

 columella light chocolate-color, with a darker margin oi' semi- 

 lunate portion posteriorh* ; grooves within the outer lip dark 

 chocolate. Adults attain 4 inches in length. 



Gulf of California to Panama; Isle of Bourbon (Deshayes) ; 

 Philippines (Cuming) ; West Indies. 



There can be no doubt of the verj- extensive distribution of 

 this species in tropical and subtropical latitudes. Dr. Gould 

 has distinguished the Pacific specimens by characters derived 

 from depauperate or immature shells, under the name of P. pansa ; 

 but well-developed forms do not difter from those of the West 

 Indies. In young individuals tlie revolving ribs and tubercles 

 are much sharper than in adults. This species does not inhabit 

 the Mediterranean, althougli so stated by several authors. 



