San Francisco Bay, were not in evidence there later. Higgins (1940) observed 

 that during the last few years the oyster drill has become very abundant and 

 destructive in the waters of Long Island Sound, Stauber (1943) observed relatively 

 high concentrations of egg cases in Delaware Bay in 1937, and relatively low 

 densities during the following three years. 



Whether such fluctuations are haphazard, or cyclical and predictable in 

 nature, can only be determined from careful quantitative studies carried out over 

 a period of decades . Should such drill population trends prove to be predictable, 

 this information would be of great value in control, 



ABUNDANCE 



A limited number of reports on the concentration of LK cinerea in a 

 variety of habitats indicate that during the summer months the drill tends to 

 occur most densely on intertidal reefs, piling, rock surfaces, and on oysters 

 on oyster bottoms, undoubtedly a reflection of its negatively geotactic response 

 at these temperatures . On subtidal oyster grounds in Delaware Bay, New Jersey, 

 an average of approximately five drills per square meter was removed on baited 

 drill traps in 1936 from a 20 acre plot (Stauber, 1943) . Since this method of capture 

 does not remove all of the drills, actual concentrations were probably higher . 

 Mistakidis (1951) obtained a maximum density of 6 drills and an average density 

 of about two drills per square meter on a subtidal oyster ground in the River Grouch 

 and Roach, England. On a relatively flat piece of intertidal bottom in Little Egg 

 Harbor, New Jersey, T. C. Nelson (1922) counted 29 drills per square meter. In 

 1953 the writer encountered concentrations of adult drills as high as 344 per square 

 meter on the vertical intertidal surfaces of encrusted rocks off the west end of 

 Gardiners Island, New York . The highest densities so far reported are those 

 recorded by Stauber (1943). He obtainted counts ranging from 237 to 947 drills per 

 square meter on an intertidal oyster reef several hundred square meters in size 

 growing on a slag pile surrounded by sand in Delaware Bay. 



The briefness of this section is an accurate reflection of the paucity of 

 quantitative data available on the density of drills Further information, but mostly 

 of a qualitative nature, is presented in the section on "Distribution" . 



FORM AND FUNCTION 



General 



A large part of the information available on the anatomy of the oyster drill 

 has been reported by the writer (1943). This, although dealing with many of the 



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