168 Binney on the Naked Air-Breathing Mollusca 



succulent plants, and sometimes ripe fruits ; they feed during 

 the night, and are rarely found out of their retreats in the day 

 time. Their growth is rapid, the animal exuded from the 

 egg in the spring, arriving at full maturity and producing eggs 

 before the succeeding winter. They are active in their mo- 

 tions, and soon escape when disturbed. They defend them- 

 selves from injurious contact by instantly secreting at the part 

 touched a quantity of milky-white, glutinous mucus, and 

 suspend themselves, head downwards, and lower themselves 

 from plants and fences by forming a mucous thread which 

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

 occasionally seen in this situation in rainy weather. During 

 the process of exuding the mucous thread, the alternate un- 

 dulating expansions and contractions 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 varies very much in color, and descriptions by 

 different authors relying principally upon it, differ greatly 

 from each other ; but whatever may be the color, the peculiar 

 character of the furrows and tubercles remains constant. In 

 a state of contraction, the back is arched, the head is entirely 

 withdrawn under the mantle, the glands of the skin are very 

 prominent, making the surface 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 disap- 

 pears when the animal is fully extended. When in motion, 

 the head extends considerably beyond the mantle, and there 

 is an interval between its margin, and the base of the superi- 

 or tentacle, equal to the length of the tentacles. The mantle 

 adheres to the body by its posterior central portion, and it is 

 in this part of it that is found imbedded the testaceous rudi- 

 ment, or shell. This is oval, curved above, very thin and 

 delicate, having a transparent epidermis. At its posterior 

 part there is a slight apicial prominence and the appearance of 

 indistinct concentric lines of growth. 



In the Philadelphia variety, the tubercles and furrows are 

 less strongly marked than in that found in the neighborhood 

 of Boston. 



