Among the numerous very large females above 41 mm. in height which he examined 

 only two or three contained exhausted gonads, while those up to 41 mm. were 

 observed depositing egg cases , Since the latter, according to Cole ; -*were probably 

 not less than 10-12 years old, the reproductive life of the female, ignoring the 

 first two years of life when a few cases may be deposited, may extend over 7 

 years Pope's (1910-11) earlier estimate of three years for the length of life 

 of the drill in Massachusetts may be too low. 



A few observations have been reported on the rate of mortality among 

 oyster drills . Stauber (1943) encountered percentages as high as 90% of empty 

 drill shells on vacant bottom in Delaware Bay. ''Most of these empty shells were 

 inhabited by hermit crabs and undoubtedly represented accumulations over a period 

 of years . 



Stauber also reported an accelerating death rate of drills during the winter 

 on grounds on which drill dredging had been performed periodically throughout 

 the winter and spring at water temperatures below which drill migrations occur 

 On one oyster bottom the mortality rate increased from 5% in December to over 

 30% in March Stauber (pers . com.) concluded that the increase in mortality 

 resulted at least in part from the action of the dredge in dislodging and exposing 

 to predation those hibernating drills which remained on the bottom. This is 

 corroborated by observations in England which disclosed that Urosalpmx car, with- 

 stand unusually cold winters (Orton, 1932) and others in America that at low water 

 temperatures (especially below 5"C) drills become progressively more sluggish and 

 slow in righting themselves after dislodgment (Carriker, 1954). 



Food and Food Procurement 

 Food preferences 



Although the oyster drill displays some discrimination m its choice of food,, 

 it feeds upon a wide variety of ammal species: its own kind, slipper limpets, 

 edible and ribbed mussels, soft and hard clams, scallops, oysters, small crabs, 

 the carrion of fish, and on such lower invertebrates as encrusting bryozoans 

 (Pope, 1910-11; Fedenghi, 1931c; Haskin, 1935; Galtsoff et al., 1937; Engle ; 1940; 

 Carriker ; 1943, 1951), On the whole its diet appears to consist principally of small 

 oysters, edible mussels, and barnacles when these are available (Galtsoff et al., 

 1937; Cole, 1942; Stauber. 1943). The effect of the relative abundance and access- 

 ibility of food species on the selection of prey is poorly understood, but it may be 

 conjectured that these factors also influence the diet of the drill 



Among the burrowing bivalves the younger dissoconch stages are attacked 

 when they are partially exposed, which occurs commonly rJuring the byssal stages , 

 Urosalpmx does not generally burrow during the warmer months of the year when 



48 



