Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 JANTHINA.—NERITA. 51 in the form of the animal. It has no oper- culum, but carries on its foot a substantial vesicular organ, which resembles froth bub- bles, which hinders it from crawling, but en- ables it to float on the surface of the water. Its head is in the form of a trunk, and has a forked tentacle on each side. The common ^^5^, species—Janthinafragilis—with a very thin violet-coloured shell, is very common in the Mediterranean, and t
Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 JANTHINA.—NERITA. 51 in the form of the animal. It has no oper- culum, but carries on its foot a substantial vesicular organ, which resembles froth bub- bles, which hinders it from crawling, but en- ables it to float on the surface of the water. Its head is in the form of a trunk, and has a forked tentacle on each side. The common ^^5^, species—Janthinafragilis—with a very thin violet-coloured shell, is very common in the Mediterranean, and the seas of all warm regions. Great numbers of them are frequently met with in per- fectly calm weather floating on the surface of !he ocean. When the animal is touched, itejects a deep violet-coloured liquor, which dyes the water all round it. The vesicular or froth-like buoy is about three limes the size of the animal; it is in the form of a cone, projecting from one side. 45, The Nerit^ are distinjjuished by the columella being a straight line, which makes the aperture of the shell either semi-circular or semi-ellipticaf. They are divided into Natica, in which the shell is umbilicafe {fig, 20, page 34) and the operculum horny; into Nerita^ properly so called^ in which the shell is not umbili- cate, thick {fig. 55), and the o])erculum stony, and into Neritina, in which the shell is also without an umbilicus, very
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