* LOCALLY INTRODUCED SPECIES. 455 



turbed. Suspending themselves, head downwards, they lower them- 

 selves from plants and fences by forming a mucus thread, which they 

 attach to the point from which they hang. They are occasionally 

 seen in this situation in rainy weather. During the process of excret- 

 ing the mucus thread, the alternate undulating expansions and con- 

 tractions of the locomotive band of the foot are seen to take place in 

 the same manner as when they are in motion on a plane surface. 



This species is much more prolific than the others, the number of 

 eggs deposited during the year being sometimes several hundred ; its 

 numbers, in favorable localities, are therefore very great. It begins 

 to lay its eggs early in the spring, and continues, with intervals, until 

 checked by the cold of approaching winter. The last deposit of them 

 often remains in the soil until the succeeding spring, when they are 

 hatched with the first generation of the year. The eggs are semi- 

 transparent and nearly globular. They produce young in about 

 twenty days after they have been deposited. 



M. Bouchard-Chantereaux has observed them to deposit eggs in 

 sixty-six days after their own birth, and to attain their full size in 

 eighty-two days. 



This species varies very much in color, and the descriptions by 

 different authors, being drawn principally from it, differ greatly from 

 each other; but whatever may be the color, the peculiar character of 

 the furrows and the tubercles remains constant. In a state of contrac- 

 tion the back is arched ; the head is entirely withdrawn under the 

 mantle ; the glands of the skin are very prominent, making the sur- 

 face appear rough ; the carina is more apparent ; and the posterior 

 extremity, being a little turned to one side, appears to be oblique. 

 It is described by some authors as constantly oblique, but the obliquity 

 disappears when the animal is fully extended. When in motion the 

 head extends considerably beyond the mantle, and there is an interval 

 between its m.irgin and the base of the eye-peduncles equal to the 

 length of the tentacles. The mantle adheres to the body by its poste- 

 rior central portion, and it is in this part of it that is found imbedded 

 the testaceous rudiment or shell. This is oval, curved above, very 

 thin and delicate, having a transparent epidermis. At its posterior 

 part there is a slight apical prominence and the appearance of indis- 

 tinct concentric lines of growth. 



There is no considerable variation in the species except in regard to 

 color, which varies almost infinitely. 



Jaw wide, low, slightly arcuate, with broad median projection. 



