and fragments of shells, the byssal threads holding them together. 

 One species varies from this rule, and simply spins a byssus. This 

 is the Modiola plicatida, a yellowish shell found on the Atlantic coast 

 of the United States. This jlfodiola uses its foot like a snail, and has 

 been seen to crawl up the side of a glass jar. 



" The mussels are of great importance and value economically, 

 thousands of bushels of the edible mussel, Mytilus edidis, being con- 

 sumed annually in Europe. They are also used as bait, millions being 

 taken for this purpose. An ingenious method of fishing for mussels 

 is used at Kiel, Germany. Boughs of trees are placed in the Bay of Kiel 

 and allowed to remain for three, four, or five years, at the end of which 

 time they are covered with mussels. Between December and March 

 they are taken up and sold by weight. The mussels are said to attain 

 their growth in a single year. 



" Still another interesting mussel is the date shell, or Lithodomus, 

 so called from its habit of boring a ' stone house ' in corals, or even 

 in the hardest limestone rock. Its burrows are shaped like the shell, 

 which prevents it from turning around. They are like the mussels 

 in form, and are considered a delicacy by some of the inhabitants 

 of the shore of the Mediterranean Sea. The perforations which this 

 animal has made in the Temple of Serapis at Puteoli have shown that 

 the sea-coast has materially changed in modern times. 



u We must now hurry on, and pass hastily by several cases which 

 we cannot study to-day. Here in this case is a large collection of ark 

 shells, with their peculiar multidentate hinge. They live at low water, 

 under and about stones, to which they anchor themselves by a byssus. 

 In the same case are a number of the nut shells, Nucula, and a related 

 genus, Yoldia, the shells of which are smooth and polished. These 

 animals live in large quantities in bays and in the mouths of rivers, 

 buried in soft mud. We must also pass by the Astartes, with their 

 brown and chestnut shells, many of w r hich are plaited like a lady's skirt. 



u We will pause a moment, however, and study the handsome shells 

 of the family Lucinidce, which embraces about one hundred and fifty 

 species of rather solid, whitish shells, beautifully ornamented with fine 

 lattice work, or straight radiating ribs. The species of this family dwell 

 principally in temperate and tropical seas, and love muddy and sandy 

 bottoms. They have been found from low water to very great depths. 

 The foot of the principal genus (Lucina) is hollow; is frequently twice 

 as long as the shell, and is folded back upon itself and hidden between 

 the gills. Several handsome species of Lucina inhabit the shores of Flor- 

 ida, notably Lucina ticjrina and Lucina chrysostoma." 



77 



