estuaries since "Brackish water species are kept within certain spatial limits 

 by the effects of the extremes of salinity and of their duration, not by the means" 

 (Stauber, 1943a). 



. Engle (1953) in a further analysis of Federighi's (1931c) data, points 

 out that Federighi records only one case in which a total mortality of drills 

 occurred at low salinities, and in all the other tests 10% of the drills survived 

 the so called death point salinity. In defense of Federighi's method Stauber (pers. 

 com.) notes that the use of the 50% mortality point is the approach of the labor- 

 atory physiologist, lather than that of the ecologist to whom 10% survival may 

 mean repopulation of an area . In an extension of the work of Federighi and in an 

 effort to determine the duration of survival of 100% of the drills at various tempera- 

 tures and salinities Engle (1953) collected drills in waters characterized by a 

 salinity range of 22 to 27 o/oo, and exposed each of groups of drills to a different 

 salinity in a series ranging from 3 to 27 o/oo for a period of about a month in the 

 laboratory in Annapolis, Maryland. In order to determine the influence of temper- 

 ature on drill survival at each of these salinities, he established the salinity series 

 in quadruplicate and exposed each series to one of the following mean temperatures: 

 17.5, 18.2, 20.1, and20.5°C. Some of these results are tabulated in Table 12 . 

 Engle discovered that all salinities below 14 o/oo were lethal to all drills within 

 the temperature range of 15.4 to 23.0°C, but that death came more slowly at lower 

 temperatures. All drills in salinities of 16 o/oo or above survived the 30 day 

 experimental period without ill effects. The death time in salinities of 14 o/oo and 

 below increased with increasing salinities and with decreasing temperatures (see 

 Table 12). Experiments at temperatures intermediate between those given m 

 Table 12 produced death times also intermediate between the values given there. 



Table 12 . Death Rates of Uro salpinx cinerea as 

 Affected by Temperature and Salinity 

 (After Engle, 1953) 



Time in Days During Which 100% 

 Mortality of Drills Occurred in 



Mean the Following Salinities: 



Temperature 



°C 7.5 o/oo 10.0 o/oo 12.0 o/oo 



17.5 13 22 30 



20.5 7 9 12 



66 



