General Chiss'ijication of the Pelecr/poda. 



105 



There are two apparent objections to Bernard's con- 

 clusions. The first is Noettling's {17, p. 87), who, in criti- 

 cizing Bernard's statement that the dorsal primary lamellae 

 of the Heterodonta appear later than the ventral ones, 

 says: — "The view that the dorsal primary lamellfe are older 

 than the ventral ones is . . . supported by the fact that the 

 Bivalves grow in a ventral direction — in other words, the 

 ventral portions of a bivalve shell are younger than the 



Fig. 9. 



LA 21 



LP I 



LAI 



LMt 



dorsal ones ; it would be certainly strange if the opposite 

 took place with regard to the hinge, where the ventral parts 

 would be the older and the dorsal parts the younger ones— 

 that is to say, the hinge would grow just' in the opposite 

 direction to the remainder of the shell.'' This certainly 

 Mould be strange, but Dr. Noettliug overlooks three facts : — 

 Firstly. That, as is shown by the growth-lines, the teetH 

 are formed entirely by secondary thickening which may take 

 place at any point. 



