6 



PROCEEDINGS OF THE NATIONAL MUSEUM 



Material. — The nujnber, source, and collection data for the speci- 

 mens examined dm:-ing this study are as follows: 



When the lengths of shells of females in the collection are plotted as 

 a function of shell height, the points form 4 discrete clusters repre- 

 senting 4 developmental stages (fig. 1). As seen in figure 1, consider- 

 able space exists between the smallest instar and embryos obtained 

 from the brood chamber of a gravid female. The space is interpreted 

 as showing that 1 or more of the younger female instars are missing 

 from the collection. By using Przibram's growth factor of 1.26, which 

 predicts the theoretical difference of a linear dimension in 2 consecutive 



