THE NAUT1LU8. 17 



The Bifidaria contracta from Florida form a race in which the 

 inner portion of the parietal lamella is divided from the forward part 

 by a depression, as if it were another lamina joined to the main one. 



In picking them over, one has a tendency to divide each lot of 

 Bifidaria pellucida hordeacella from Florida into four forms, figured 

 on plate II, as follows: form A, long, figs. 1. 3, 4, 5, 9, 10, 15; 

 form B, medium-sized, tigs. G, 7, 8, 13, 16, 17, 19; form C, small, 

 tigs. 14, 20, 21, 24, 25, 26, 27, and form D, obese, tigs. 12, 18, 22. 

 All these forms seem to intergrade in size through a small number of 

 examples. The variation observed is largely due to the formation of 

 a lip when the shells have made a different number of volutions, as 

 the long forms have about 5^ whorls and the short forms only about 

 4 whorls. It is peculiar that the long shells from Florida have weak 

 teeth and the short specimens have strong teeth ; while in Texas 

 the converse is often the case. 



To give an idea of the relative abundance of the forms, in a lot of 

 Bifidaria p. hordeacella from Bahia Honda Key I counted 25 long, 

 31 medium, 15 small, and 7 obese shells. In another series from 

 Key West there are 111 long, 358 medium, 22 small, and 140 obese 

 specimens. Each of these lots was from dirt gathered in the area of 

 a square yard or less. The size in mm. of the several forms may be 

 measured by the scale supplied on the plate. 



Vertigo variolosa is very scarce, as only four perfect specimens 

 were found. Helicina tantilla also continues to be excessively rare. 

 Many other equally small species were obtained by thousands. 



For lists of species from other keys visited, see the THE NAUTI- 

 LUS, xix, 1905, p. 38, and xxi, 1908, p. 99. Altogether over 50,- 

 000 specimens have been picked from dirt and debris obtained on the 

 Florida Keys. 



BAHIA HONDA KEY, Lee Co., collected by Dr. H. A. PiLsbry. 



Chondropoma dentatum Say. 



Truncatella bilabiata Pfr. 



Truncatella caribaeensis succinea Ad. 



Thystmophora selenina Gld. 



Thysanophora plagioptycha Shutt. 



Polygyra cereolus MUhl. 



Polygyra cereolus carpenteriana Bid. 



Pupoides modicus Gld. 



Bifidaria p. hordeacella Pils. 



