THE CUP-AND-SAUCER LIMPETS. 331 



Cassis, or Queen Conch, the Doliums, and the exquisite Ranellas all are of this order, under 

 their respective sub-orders. In this enumeration are some of the most valued of shells as well 

 as most beautiful. Many of the Cones are of great value as rarities, and the Strombi and 

 Cassids are of considerable value commercially. 



In our waters there are not many of especial interest excepting to the student. Our semi- 

 tropical waters, however, bear some of marked beauty. The most beautiful Queen Conch 

 (Cassis madagascarensis) has been found frequently on the Florida Reef, and along the coast 

 as far as Charleston. The Bahamas are good localities for these and the large Strombi that 

 are used in cameo-cutting. The great Horse Conch (Strombus gigas) is abundant in Florida 

 waters, and it is very beautiful when first removed from the water ; its rich colors fade quickly 

 when the animal dies. Several species of Volutes are common on the Reef and along the west 

 coast of Florida. Olivas are also found. The Murex, in many species, is found, though 

 sparsely, but of exceeding beauty and singularity of structure or ornament. On the New 

 England coast and on the Grand and Georges banks are many interesting forms, though none 

 of great beauty. The smaller Buccinums are common, and many interesting shells are found 

 in the stomachs of fishes. 



THE well-known univalves, so familiar under the name of Limpets, are divided into 

 several families, on account of certain variations in the structure of the shell. The first family 

 is termed Fissurellidse, on account of the fissure which appears either at the apex or in the 

 front edge of the shell. 



All the Limpets are strongly adhesive to rocks, as is well known by every one who has 

 tried to remove one of these mollusks from the stony surface to which they cling. The means 

 by which the animal is able to attach itself with such firmness is analogous to the mode in 

 which the suckers of the cuttle-fish adhere to the objects which they seize, the formation of a 

 vacuum, and the consequent pressure of the atmosphere, being the means employed. The foot 

 of the Limpet is rounded, broad, thick, and powerful ; and when the animal wishes to cling 

 tightly to any substance, it presses the foot firmly upon the surface and retracts its centre, 

 while its edges remain affixed to the rock. A partial vacuum is therefore formed, and the 

 creature becomes as strongly attached to the rock as a boy' s leathern sucker to the stone on 

 which he has pressed it. 



The KEY-HOLE LIMPET is so called on account of the aperture at the top of the shell, 

 which serves as a passage through which is expelled the water that has passed over the gills. 

 This aperture is found in all the species of the genus Fissurella, but varies greatly in form 

 and comparative dimensions, being, in some cases, a mere rounded hole in the shell, while in 

 others it is a long and curiously-shaped aperture, very like the key-hole of a lock. The 

 aperture increases with the shell, being hardly perceptible when the animal is young, but 

 encroaching rapidly until it removes the whole of the sharp apex. These animals are mostly 

 found at the same depth with the great tang sea- weeds, but are sometimes to be taken in fifty 

 fathoms of water. Tlue genus Fissurella is a large one, comprising about one hundred and 

 twenty species. 



The curious DUCK-BILL LIMPET inhabits the hotter seas, and is found on the shores of 

 New Zealand, the Red Sea, and the Cape. It belongs to a small genus, containing about ten 

 species. 



This shell derives its name from its peculiar shape, which certainly does bear some dis- 

 tant resemblance to the beak of a duck. The animal is of very great comparative dimensions, 

 and while living covers the shell with its mantle. Its color is black, and its sides are edged 

 with short fringes. The eyes are set on the outer bases of the tentacles. The color of the 

 shell is very pale yellow. 



A number of nearly allied shells, belonging to the same family as the preceding species, 

 are called CUP-AND-SAUCEK LIMPETS, from the peculiar cup-shaped process on the interior, 

 the shell itself taking the place of the saucer. This process forms the base, to which are 

 attached the muscles which draw the animal to the rock. None of these Limpets appear to 

 be active, seldom quitting the spot on which they have settled themselves in their infancy. 



