temperatures approximated those out of doors and on bottom prepared to simulate 

 a natural one in the field. Field observations consisted of a study of the vertical 

 disposition of drills in a natural population in Shark River and of drills caged over 

 bottom in a tidal pond on Gardiners Island, New York . 



Field and laboratory observations disclosed that in general during the 

 winter drills remain attached to hard surfaces, and their vertical distribution 

 ranges from those stationed somewhat superficially in the hollows of upturned 

 empty shells to those completely buried in the bottom. Adherence of the drill 

 to the substratum is noticeably weaker at lower temperatures, particularly below 

 S^C, and considerable variation occurs in the degree of torpor exhibited by differ- 

 ent drills. 



Laboratory studies revealed that drills burying in the sediment may move 

 backward into deep sediments along vertical hard surfaces or creep forward in 

 shallow sediments but go no deeper than the siphon tip. In every instance observed 

 this remained just above the surface of the bottom in contact with the water. No 

 dull was ever seen in the process of creeping backward or forward into deep 

 sediment, but numerous drills buried to different depths, always with the siphon 

 tip upward, were seen repeatedly, and in no case was the sediment appreciably 

 disturbed immediately around the drills suggesting that the drills had moved into 

 the bottom siphon tip forward and then turned. The question also anses as to 

 whether a drill would block its siphon with sediment if it should move siphon end 

 first into the bottom . It was also observed that in uneven bottom drills frequently 

 bury at the lowest level in depressions and thus may come to lie some distance 

 below the general level of the bottom . At least 75% of the drills buried partly or 

 completely m the bottom during the colder months of the year . Those remainmg 

 on the surface generally placed themselves in the hollows of empty shells and under 

 these shells and soon became obscured by silting Considerable variation occured m 

 "the locomotory activity of different drills during the winter . A few started burying 

 in the bottom at temperatures above 10 a C. Temperatures below 5°C reduced drill 

 movements onto the sides of the aquarium almost to zero, sometimes after a lag of 

 a few days, and in general suppressed such movement for as long as 10 days even 

 though in the interim water temperatures again rose intermittently as high as 13° C. 

 During the coldest period of the winter when water temperatures fluctuated between 

 1.6 and 4.0°C, the arrangement of the drills did not change appreciably, except 

 that exposed drills moved a little deeper among the shells and became less evident. 

 Individually marked buried drills also exhibited great, though localized, variation 

 in movement throughout the winter at temperatures approximately above 2°C. 

 Many of those only partially buried moved deeper or horizontally or completely 

 vacated the hibernation site for another, or did not bury again, Drills buried to 

 the siphon tip likewise moved horizontally or upward, and often sought other 



72 



