MOLLUSCS, OE SHELL-FISH. 241 



scarlet, and may occasionally be found flung ashore after 

 storms. 



Before passing to the siphonate Azygobranchs, we must 

 mention one other form not uncommon in some places 

 between tide-marks which is very different in appearance 

 from its allies. This is Lamellaria perspicua, especially 

 interesting because the shell is very thin, and is completely 

 covered by the mantle. This reduction of the shell occurs 

 in many different sets of Gasteropods, but is rare in the 

 littoral Azygobranchs. In Lamellaria the body is very 

 convex, without external trace of shell, is usually yellowish, 

 but may be white or purplish. The head bears two tentacles, 

 with small eyes at their bases. The animal is very active, 

 and may reach a length of two inches, but between tide- 

 marks specimens are usually of very much smaller size. It 

 is possible, by very slight dissection, to find the concealed 

 shell which lies in the middle of the back, .and is of a 

 delicate white colour, with a mere trace of a spire. The 

 living animal is apt to puzzle the beginner very much, for it 

 has few characters which can be very definitely laid hold of, 

 and specimens between tide-marks are not infrequently of 

 very small size. On the dorsal surface notice the rounded 

 mantle, often highly spotted and marked, and with a very 

 characteristic notch anteriorly over the head, which serves 

 as a kind of siphon to admit water to the small chamber in 

 which the gill lies. When the animal crawls it trails a 

 translucent foot behind it, while the long, slender tentacles 

 project in front. If it be turned over, the broad, creeping 

 surface of the foot will become very obvious, and also the 

 large, black eyes at the base of the tentacles. The animals 

 are to be found under stones between tide-marks, and on 

 account of the activity of their movements are very charm- 

 ing occupants of an aquarium. 



Of the carnivorous siphonate Azygobranchs, the common 

 Purpura lapillus is perhaps the most abundant 011 the shore. 

 Like many of its allies it yields a purple dye similar to 

 that which furnished the ancients with their famous Tyrian 

 purple. In some places it is called the dog-periwinkle, and 

 is one of the most variable of shore animals, and one of 

 the most abundant. It is purely an inhabitant of the 

 littoral zone, and lives upon other Molluscs, chiefly Bivalves, 

 B 



