VARIATIONS IN THE PALLETS 



OF TEREDO NAVALIS IN 



SAN FRANCISCO BAY 



BY 



ROBERT CUNNINGHAM MILLER 



INTRODUCTION 



During the course of the study of variations in the shell of Teredo 

 navalis in San Francisco Bay (Miller, 1922), an investigation was 

 made as well of variations occurring in the pallets of this species. 

 The results of this investigation were for several reasons not incorpo- 

 rated in the published results of the earlier study. As every collector 

 of this group of mollusks is aware, it is extremely difficult to secure 

 good series of pallets which have not been damaged by accident or 

 erosion to such an extent as to render them unsuitable for a study of 

 physiological variation. In the rather limited number of normal 

 and well preserved pallets available in our collections, it was found 

 that the index of individual variation was extremely high. The types 

 of variation observed were not at all so definitely correlated with 

 ecological conditions as is the case with shells. Finally, variations 

 in the pallets, although very striking as matters of observation, are 

 not of such a nature as to lend themselves to statistical treatment. 

 For these reasons it did not seem pertinent to include remarks on the 

 pallets in our discussion of variations in the shell. 



After the earlier paper had gone to press, however, there came 

 to hand Bartsch's recent (1922) monograph of American shipworms, 

 in which certain minor differences in the pallets of Teredo are 

 regarded as being of considerable systematic importance. One 

 species, indeed (Teredo beau for tana), is offered for acceptance on 

 the basis of pallets alone, the shell having not yet been discovered ; 

 and in several other instances slight deviations in the pallets are 

 emphasized to such a degree as to constitute what seems to be, to say 

 the least, an impracticable precedent. It is perhaps desirable, there- 

 fore, to set forth at this time such data as we have on variation in 

 the pallets of Teredo navalis in San Francisco Bay, because of their 

 bearing on the systematic treatment of the entire Teredo group. 



