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BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



along the western coast of America ? To establish this would require 

 an extensive series of collections off the coast of Central and South 

 America, and comparisons of the faunas at the same latitudes on the 

 two sides of the Pacific. But, if it is true, it emphasizes the necessity 

 of recognizing this fact in fisheries investigations and demonstrates 

 an essential difference between the problems, economic and otherwise, 

 of the coastal waters of the eastern and western Pacific. 



That the chaetognath faunas of the two regions are fundamentally 

 different is made more certain by the fact that in four of the five 

 Sagitta 1 common to both Philippine and San Diego regions, the 

 Philippine specimens have a greater number of both anterior and 

 posterior teeth. The same is true with respect to P. draco, and in 

 E. hamaia the Philippine specimens have nearly twice as many 

 teeth (21 to 25) as do the San Diego specimens (10 to 13). These 

 differences are mentioned in the preceding pages in connection with 

 the account of each species, but are better revealed, perhaps, in the 

 following list: 



Species. 



S. enflata 



8. neglecta 



S. serratodentata 

 S. plankton is... 

 P. draco 



Anterior teeth. 



Posterior teeth. 



Philippines. San Diego. Philippines. San Diego 



6-11 

 4-8 

 8-11 

 6-10 

 6-10 



4-8 

 3-5 

 6-9 

 4-7 

 4-4 



9-15 

 12-16 

 13-24 

 12-18 

 10-16 



7-12 

 8-11 

 13-19 

 11-15 

 8-9 



In the case of P. draco the differences may mean little, owing to 

 the fact that only a single very immature specimen is recorded from 

 the San Diego region. It is interesting, however, to note that it was 

 7 millimeters in length, whereas 15 of the 20 from the Philippine 

 region recorded in Table 17 are smaller and quite as immature, the 

 smallest being less than 5 millimeters in length, although it has 

 6 to 7 anterior teeth and 13 posterior teeth. 



To demonstrate that the differences in number of teeth given for 

 the four species of Sagitta are significant, from 10 to 30 or more 

 individuals of each species were selected at random from the two 

 collections, the number of teeth counted, and the mean number and 

 corresponding probable errors computed. The results are entered in 

 Table 19: 



Table 19. — Comparison of mean number of teeth in specimens from the Philippines and 



from the San Diego region. 



1 S. heiaptera is not considered owing to loss of teeth. See p. 245. 



