166 MALACOZOA. GASTEROPODA. PECTINIBRANCHIATA. 



GENUS 3. PURPURA. WHELK. 



Animal elongated; the body spiral; the head large, 

 with two approximated tapering, flattened tentacuia, 

 supporting the eyes on an enlargement at their middle 

 externally ; the proboscis short ; the foot large, broad, 

 two-]obed anteriorly ; the operculum semioval, horny. 



Shell ovate, thick, with the spire short, the last whorl 

 very large, its breadth being at least three times the 

 length of the spire ; the aperture elliptical or semioval, 

 with the outer-lip thin-edged, the columella flattened, 

 and often ending in a point anteriorly, the canal short 

 and wide. 



Marine, inhabiting the rocky shores. The genus 

 obtains its name from the purple dye yielded by some of 

 the species. 



1. Purpura Lapillus. White WhelJc. 



Shell ovato-fusiform, thick ; with the spire small and pointed ; 

 the turns convex, the last very large, longitudinally ribbed, 

 transversely lamelloso-striate ; the aperture elliptical ; the outer 

 lip thin-edged, undulated or denticulate, and somewhat grooved 

 internally ; the columellar lip rather flattened, externally trans- 

 versely rugose ; the notch small, a little recurved ; the colour 

 generally white, the mouth tinged with purple. Length an 

 inch and four- twelfths, breadth seven-twelfths. 



Animal with the tentacuia tapering and depressed, with the 

 eyes situated in a notch near their middle on the outer side ; 

 the proboscis short ; the foot oval, yellowish, with the brown 

 horny operculum placed on its back. The fluid which yields 

 the purple colour is found in a vessel on the back of the animal. 

 It is of a yellowish-white colour, but on being exposed to the 

 air becomes bright yellow, then pale green, bluish-green, and 

 purplish-red. It has been used for marking linen. 



The nidus is an oblong, somewhat cup-shaped, semitrans- 

 parent yellow cartilaginous sac supported on a short pedicel, 

 attached to a rock or stone, and covered with a convex lid. 

 It contains a viscid fluid, in which are numerous ova, which 

 on being developed so as to present a regularly-formed shell 

 of four turns, make their escape by the bursting of the lid. 



The shell varies in colour, individuals being grey, purplish, 

 yellow, brown, black, purple, pink, or white, plain or variously 



