316 E. M. NELSON ON AMPHIPLEURA LINDHEIMERI. 



The length-breadth ratio in the new form is 7*5, and in the 

 old 8-5. 



The conditions here are therefore opposite to those we found in 

 Naviada rhomboides,* for those with the greater ratio had the 

 coarser striae, but in this case they have the finer. 



If we divide the ratio by the number of striae in T ff ^th of an 

 inch we shall obtain a numerical index of about 1*1. Thus : 



Old Lindheimeri : Ratio 8*5, striae 7*7, index l'l. 



New Lindheimeri : Ratio 7 '5, striae 6*7, index l'l 2. 



Amphipleura pellmida follows much the same rule,for "resolvers" 

 who understood the subject sought out wide valves, i.e. those with 

 a small ratio. 



* Journal Q.M.C., vol. xi. p. 97, 1910. 



Jovrn. Qv.ekclt Microscopical Club, Ser. 2, Vol. XII., No. 74, April 11)14 



