210 



Papers from the Department of Marine Biology. 



THE "WHITE HOUSE TYPE." 



In order to determine the amount of variation which has taken place 

 in the first generation of these snails born and matured in Florida, a 

 check serie's (plate 1, upper row, and plate 2, middle row) of 10 speci- 

 mens was selected from a lot of more than 1,000 from Andros Island, 

 Bahamas. These were collected at the same time and place in which 

 the specimens planted on the Florida Keys in 1912 were obtained. 

 These 10 specimens are part of a handful which was taken at random 

 from the box containing the lot, and the 10 specimens in turn were 

 picked from this handful without looking at them. We therefore 

 assume that they represent a fairly typical average series. They are 

 characterized by quite uniform outline and sculpture. 



These 10 specimens from left to right yield the data shown in table 1. 



TABLE 2. First generation of "White House 

 Type" cerions from Bahia Honda Key. 



TABLE 1. Check series "White House 

 Type" cerions. 



*This measurement in each case is the 

 diameter of the shell from just back of 

 the lip to a point diametrically opposite. 



tLength estimated. 

 JShell not quite adult. 



A comparison of these first Florida generation shells (plate 1, lower 

 row) with the check (Bahama parent generation) series (plate 1, upper 

 row) shows that the general outline and sculpture seem to have been 

 maintained, but the texture of the shells has a more glossy and harder 

 appearance. The measurements show an increase in the number of 

 whorls a greater altitude with a greater range of variation. In the 

 check series the total variation was 4 mm. In the Florida-born off- 

 spring it is 8.3 mm. The diameter has also increased materially, and 

 with it the range of variation. In the check series this is 1.3 mm.; 

 in the above, 2.3 mm. We may, therefore, say that the first generation 

 from Bahia Honda, Florida, represents a much more variable organism 

 than the parent stock in the Bahamas. 



