162 Annals of the Carnegie Museum. 



Table I. — Continued. 



6 and 7. Length of anterior {AHL) and posterior (PHL) part of 

 the hinge measured from the beak, giving the total hinge-length, by 

 means of a steel-rule. (Scientific Materials Company Catalog No. 

 3946). Where the hinge-line curved, it was possible .with practice to 

 estimate the length. 



8. Thickness of the valve just superior to the pallial line, in the 

 region directly beneath the umbo. It was thought that such a 

 measurement might be more easily correlated with the other dimen- 

 sions taken. This was secured with a micrometer-screw caliper. 

 (Scientific Materials Company Catalog No. 3934.) 



