112 VARIATION IN THE SHELL OF PTEROCERA LAMBIS, LINN. 



It can be identified, I think, with absolute certainty, with one of 

 the digitations of P. miUepeda, Linn., namely, the fourth. I 

 obtained four specimens of P. miUepeda, which has nine labial 

 digitations, from New Guinea. In two of these the fourth 

 digitation was markedly smaller than any of the others, while 

 agreeing in position with that above described in P. lambis. In 

 fact, in 7-*. millejyeda the intercalated digitations are obviously the 

 second and fourth, and probably the seventh. 



It may also be remembered as indicating the significance of 

 the appearance, by variation, of an extra digitation in P. lambis, 

 that in P. elongata, Swainson, there are eight labial digitations, 

 in P. tnolacea, Swainson, ten, and in P. chirayra, Linn., five. 



EXPLANATION OF THE FIGURES. 



Fig. 1.— The canals leading into the tubular digitations are still open, the 

 deposition of callus having only commenced. 



Figs. 2 and 3. —The canals are closed up by callus, their previous existence 

 being indicated by shallow furi'ows. 



i.d., intercalated digitation. 



The shell represented in Fig. 1 was the same in which the apex of the 

 spire was imbedded in the posterior digitation as mentioned in the text. 



