[21] INSTRUCTIONS FOR COLLECTING MOLLUSKS BALL. 



margin of the coralline zone. For work in the deeper i)arts of the lat- 

 ter a sailboat or small tug and a crew of several men are necessary for 

 effective work, but the trouble and expense are well repaid by the rari- 

 ties which can be secured in this and no other way. 



The mollusks of the beach differ widely in different latitudes. In 

 the north Litorma, Purpura, and various limpets frequent the rocky 

 and stony shores, while near low water on the under surface of flat 

 stones and under overhanging ledges several species of Chiton find a 

 congenial home. Among the barnacles and under the profuse fronds 

 of the bladder weed small Eissoids and the urnlike ovicapsules of Pur- 

 pura are common. On the Californian coast HaUotis, Acmwa, and many 

 Chitons abound in such localities. As we go south the fauna of stony 

 beaches becomes richer, and a vast number of small shell-bearing and 

 naked mollusks inhabit them. Where there is a mixture of stones and 

 sand, large sea-anemones or Actinia live between the pebbles, often cov- 

 ered with fragments of shell and bits of gravel, amongst which careful 

 examination often reveals many small shells sticking to the adhesive 

 surface of the polyps. These mast be secured by means of the forceps, 

 as they are not easily detached. 



On the sandy beaches will be found a special fauna, without taking 

 into account the species thrown up by the waves from deeper water. 

 Natica is one of the most common gastropods, and living specimens 

 may readily be detected by the little mound of sand which they push 

 before them as they plow their way just below the surface. Nassa is 

 one of the most familiar forms in such places and, like Natica, is preda- 

 cious, living on the flesh and juices of bivalves, which it seeks beneath 

 the sand, drilling in their shells the small circular holes which may be 

 noticed in the majority of the dead bivalves strewn upon the beach. 

 In the south Fulgur is one of the largest and most common of the gas- 

 tropods characteristic of the sand beaches, and its horny coils of ovicap- 

 sules, in the shape of angular spiny disks adhering by one edge to a 

 connecting lamina, are among the most frequent objects on the shore. 

 The drills, TJrosalpinx and Eupleura, so destructive to young oysters, 

 abound in many places. The bivalves exceed all others in the number 

 of individuals. Mactra, Petricola, and Macoma in the north, with Donax, 

 Tellina, Venus, and JDosinia in the south, are among the most conspicu- 

 ous forms. Living specimens are usually concealed under the surface. 

 Small holes in the sand, by which water obtains access to their siphons, 

 indicate the spot they occupy. Advancing waves will often uncover 

 thousands of small specimens of JDonax, which disappear as if by magic 

 as the water recoils. OUvella and OUva frequent sand beaches near 

 low- water mark and also are burrowers. In Florida Strombus pugilis, 

 Melongena corona, and Pyrula papyratia are very abundant in snch 

 l^laces. 



On muddy flats, especially if somewhat sprinkled with gravel or peb- 

 bles, another set of mollusks may be found. Mya and Petricola, certain 



