216 



ZOOLOGY 



Fig. 203. — Plaiior- 

 bis, the flat-coiltM.l 

 pond snail. Nat. 

 size Photo, by 

 W. H. C. P. 



lives ill a similar habitat with Physa. A great many species 

 are known, and they vary much in size. Snails of this genus 

 likewise are easily kept in the aquarium, and 

 lay numerous eggs encased in gelatinous 

 envelopes adhering to the glass. 



Of the shells of marine gasteropods, 

 which are favorite objects in collections 

 because of their beauty and permanence, 

 only a few types can be mentioned. 



Lit'torina ^ is an example of the entire- 

 mouthed marine snails. The commonest 

 form at most jiarts of the shore-line north of New York at 

 the present time is Littorina littorca.- This is known in 

 England as the periwinkle, and is there used as food. As 

 its S3^stematic 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 occupied our shores, but has been 

 migrating southward. 



In 185-5 Littorina was found in the Gulf 

 of Saint Lawrence ; in 1869 it was stated to 

 occur in HaHfax ; 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, Massachusetts ; 

 in 1875 the first two specimens were taken at Woods Hole, 

 Massachusetts, south of Cape Cod ; in 1880 the first specimen 

 was taken at New Haven ; in 18!)1 it occurred as far south 

 as Delaware Bay. In 1899 it was not very abundant at 

 1 Fig. 204. 2 Ffoni iillus, the seashore. 



Fio. 204.— L/«i)riiio /i7- 

 lorca, the shftre snail. 

 Nat. sizo. Photo, hy 



\y. H. c. p. 



