406 University of California Publications in Zoology [Vol. 22 



ostracum than those from the middle and lower bay, which corre- 

 sponds with our observation concerning the periostracum of the shell 

 (1922, pp. 311, 312), which was found to be thicker and rougher in 

 the case of specimens from the upper bay. It may be stated also, as 

 a fact of general observation, that the chitinous tips of the pallets 

 tend to be darker in color in specimens from the upper bay than 

 in those taken elsewhere. This is not always true in individual cases, 

 as will be seen by reference to plate 20; the tips of pallets 8 b, 8 d, 

 and 8 g in the Goat Island series are almost as dark as the darkest 

 of the Crockett pallets (fig. 6 g) ; but the proportion of pallets with 

 a notably dark distal portion is greater among the pallets from the 

 upper bay. 



It should be mentioned in this connection, however, that pallets 

 taken near the mud line of a pile, or from waters containing much 

 decaying organic matter, are likely to be much stained, as was 

 observed in the shells (1922, p. 313). It is necessary therefore to be 

 cautious in interpreting such data. 



