6 DAY, Variation in a Carboniferous BracJiiopod. 



tion of the presence of more than one species in the 

 collection. 



ONTOGENY. — The specimens included shells in various 

 stages of growth. Accordingly, with the object of indi- 

 cating any possible ontogenetic changes, the shells were 

 now divided into three sets according to length. The 

 first set embraced those shells with length 0*15 to 0*45 



Length 



Fig. 2. — Curve showing the distribution of the ratio 



anions: 1000 individuals of Reticularia lineata. 



Depth 



i*9 i"8 17 i*6 1 '5 1 -4 1*3 1 2 n 



Length 

 Depth 



inch ; the second set those shells with length 045 to 075 

 inch ; and the third set 075 to 1-05 inch. 



Curves were now constructed to show the distribution 

 of s and - in these sets. The curves obtained for distribu- 



tion of 7= for each of the separate sets are shown in Fig: 3. 



