MARINE MOLLUSCS 



249 



FIG. 181. 1. Purpura lapillus. 2. 

 EGG CASES OF Purpura. 3. Nassa 

 reticulata 



clusters of egg cases are washed up in large numbers on the beach, 



where they form one of the commonest materials among the 



refuse at high-water mark. It is not uncommon, also, especially 



after storms, to find the unhatched eggs stranded by the waves, 



and these are so transparent 



that the embryos, several in 



each capsule, may be seen 



within. The hole through 



which the young escape 



may also be seen on the 



inner side. 



The Dog Periwinkle 

 (Purpura lapillus) abounds 

 on all our coasts and is re- 

 markable for the production 

 of a dull crimson or purple 

 fluid that may be obtained 

 from it by pressing on the 

 operculum. This fluid turns 



to a brighter colour on exposure to air, and is said to have been 

 used largely in former times as a dye. It will be seen from our 

 figure that the spire of this shell is shorter in proportion than that 

 of Buccinum ; but both are alike in that the operculum is made 

 up of layers with a nucleus on the external edge. 



The other species figured 

 is Nassa reticulata, popularly 

 known as the Dog Whelk, and 

 characterised by a tooth-like pro- 

 jection of the inner lip close to 

 the anterior canal. It is very 

 common near low-water mark, 

 where it may be seen crawling 

 over the rocks on its broad foot, 

 from which project two hornlike 

 appendages in front and two 

 narrow tails behind. FIG. 182. Murex erinaceus 



From the last family of the 



gasteropods (the Muricidce) we select two common species Murex 

 erinaceus and Fusus antiquus (Plate V.). In both these the 

 anterior canal of the shell is straight and the posterior wanting. 

 The eyes are on the tentacles, and there are two plumed gills. Both 



