organ systems of the animal, emphasizes the minute anatomy of the anterior 

 portion of the alimentary canal. Much of this anatomy is so detailed that it seems 

 appropriate, as a basis for a better understanding of the ecological portions of this 

 review, to include here a simplified condensation . 



The shell of U. cinerea has been illustrated in a number of publications 

 Q. K. Nelson, 1931, these drills were collected in Hueys Creek, Little Egg Harbor, 

 New Jersey; Federighi, 1931c; Galtsoff et al . , 1937; Cole, 1942; Carriker 1943) . 

 It is dextral, thick, and solid and thus affords a considerable degree of protection, 

 spirals conically, and bears spiral striations and longitudinal ribbing. A short 

 siphonal canal extends forward from the small aperture of the shell . In a series 

 of five tests Sizer (1936) determined that shell material of adults possesses a 

 salt content of 1.30 o/oo. When the animal is retracted within the shell the aperture 

 is tightly closed by a strong chitinous operculum which is borne upon the rear upper 

 surface of the foot. Just how long a drill may remain tightly sealed within its shell 

 under a variety of conditions is not known. J. R. Nelson (1931) notes that at summer 

 temperatures drills have been known to remain alive out of water for several days, 

 presumably in the shade. 



When normally expanded the exposed soft parts of the drill, consisting of 

 a small foot, head, and tentacles, extend but a short distance outward from the shell . 

 A pair of slender tapering retractile tentacles, nearly united at their bases, and each 

 bearing a jet black eye along the mid outer side, arises on the front of the head and 

 points forward. In males a long tapering "C-shaped" penis, about the length of an 

 extended tentacle, lies on the right side of the head, and because it is hidden under 

 the shell is rarely visible . 



A false mouth lies just below the base of the tentacles. The true mouth is 

 found at the tip of a long trunk -like proboscis which is normally honed within the 

 head region. The proboscis is everted through the false mouth when the snail is 

 drilling or feeding. Drilling is facilitated by two accessory structures. The first 

 consists of a tube formed by the inward overlapping of the lateral ridges of the 

 front part of the foot. The proboscis moves within this fleshy cylinder, receiving 

 support and protection therefrom when everted. The second structure is the 

 accessory proboscis, a gland lying in a cavity in the mid anterior ventral portion 

 of the foot. The opening to this cavity is very difficult to see macroscopically 

 except when the gland is functioning. In females an egg case pouchlies directly 

 behind the accessory proboscis and is visible externally as an oval constricted 

 depression. 



All external surfaces of the drill, especially the ventral surface of the foot, 

 are covered by a thin sheet of epithelium which secretes mucus and is covered with 



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