1923] Miller: Variations in the Pallets of Teredo navalis 407 



DISCUSSION AND CONCLUSION 



In the light of the foregoing data, it becomes pertinent to inquire 

 in how far deviations in the pallets are to be regarded as of systematic 

 importance. It is obvious, in view of the range of variation above 

 pointed out, that if minor differences in these structures are to be 

 looked on as specific characters, the describing of new species of 

 Teredo can be limited only by the persistence of the investigator 

 and his supply of paper and ink. 



The pallets of Teredo novangliae, according to Bartsch (1922, 

 p. 20), "expand suddenly beyond the stalk, forming a decidedly 

 concave outline," while in navalis "they expand only gradually, 

 forming an almost straight line. " It is interesting to note that from 

 one locality in San Francisco Bay we have pallets which expand both 

 gradually and suddenly, with several degrees between, the proximal 

 outlines of the blade being straight (pi. 20, fig. 6 a), concave (figs. 6 c 

 and 6d), and even decidedly convex (fig. 6 h ; fig. 8/). A similar 

 range may be pointed out in the series from Dumbarton and Goat 

 Island. It is still further disturbing to find a hybrid form nearly 

 straight on one side and concave on the other, as the pallet shown in 

 figure 6 b, plate 20. 



Concerning Teredo morsei Bartsch, we learn that "the pallets 

 are rather broad at the anterior termination of the calcareous portion. 

 The corneous portion is rather short and deeply cut. The sides 

 of the calcareous portion slope gently toward the somewhat curved 

 and twisted stalk" (idem, p. 21). No figures of this species are given, 

 but we venture to suggest that the description just quoted applies 

 admirably to the last shell in our Dumbarton series (pi. 20, fig. 7 h). 



The pallets of Teredo beaufortana are "much narrower and more 

 elongate" than "true Teredo navalis" (ibid., p. 22), this being appar- 

 ently the only character by which the two species may be distin- 

 guished. It is interesting to note the degree to which the pallets 

 figured for beaufortana approach the third pallet figured in our series 

 from Oakland harbor (pi. 19, fig. 4). 



It is rather remarkable that a specimen figured from Crockett 

 (pi. 20, fig. 6 a) should so nearly approach the type of navalis as 

 figured by Jeffreys (loc. eit.) and by Bartsch (1922, pi. 32, fig. 2), 

 when we consider that the locality in question is the type locality of 



