THE SLUG AND ITS ALLIES 167 



eggs encased in gelatinous envelopes adhering to the 

 glass. 



Of the shells of marine gastropods, which are favorite 

 objects in collections because of their beauty and per- 

 manence, only a few types can be mentioned. 



Littorina 1 is an example of the entire-mouthed proso- 

 branchs. The commonest form at most parts of thj^hore- 

 line north of New York at the present time is 

 littorea. 2 This is known in England 

 as the periwinkle, and is there used as 

 food. As its systematic name implies, 

 it occurs on the seashore, which it 

 often crowds so as to force all other 

 species from it. It occurs north to 

 Greenland, and on the northwestern 

 European coast. It has not always FIG. 155. Littorina lit- 

 occupied our shores, but has been ?* 

 migrating southward. In 1855 Lit- w. H. c. P. 

 torina was found in the Gulf of 

 St. Lawrence ; in 1869 it was stated to occur in Halifax ; 

 in 1870 a few individuals were found on the Maine coast ; 

 during 1871 the species occurred on the New Hampshire 

 coast ; in 1872 one specimen was found at Salem, Massa- 

 chusetts ; in 1875 the first two specimens were taken at 

 Woods Hole, Massachusetts, south of Cape Cocl ; in 1880 

 the first specimen was taken at New Haven ; in 1891 it 

 occurred as far south as Delaware Bay. Yet at the present 

 time it is not very abundant at Cold Spring Harbor, near 

 the western end of Long Island Sound. Persons who live 

 on the coast south of Cape Cod would do well to note care- 

 fully the abundance of the species on their part of the 



1 Fig. 155, 2 From Uttus, the seashore, 



