1911] Michael: Chaetognatha of the San Diego Region. 71 



2. S. elegans matures sexually at 23 mm., while in none of 



the specimens of S. arctica examined were the ovaries 

 even well developed, nor the seminal vesicles evident. 



3. The ovary is slightly broader and longer in *Sf. elegans. 



Outside of these points the two species are nearly identical. 

 Inasmuch as the specimens of S. elegans were preserved in 

 alcohol, and those of S. arctica in formalin, the fact that the 

 former is more flabby loses most of its significance. The other 

 two points are interdependent, for in individuals that are sexu- 

 ally mature we should expect the ovary to be slightly longer and 

 broader. Finally, as to the size at which specimens mature, we 

 have noticed considerable variation in such species as S. enflata 

 and S. hexaptera. From this evidence we are compelled to place 

 *S^. elegans and S. arctica in the same species, and as Fowler 

 (1906) has pointed out, the former takes priority, and /S^. arctica 

 becomes a synonym. 



Having concluded that the two species are synonymous it 

 remains to see whether S. elegans stands as a valid species or 

 whether it must, in turn, be placed in the synonymy of another 

 species. 



Being without a collarette 8. elegans naturally falls into the 

 group with S. enflata, S. hexaptera, 8. lyra, 8. bedoti, 8. serrato- 

 dentata, and 8. macrocephala. Being opaque and provided with 

 strong muscles it is readily separable from the first three. From 

 8. bedoti it is easily distinguished by the fact that 8. elegans 

 has more than 50 per cent of posterior fin in front of tail-septum, 

 by the presence of a considerable interval between anterior fin 

 and ventral ganglion, and by the fact that the posterior fin is 

 longer than the anterior fin. From ^S'. serratodentata it differs 

 in the absence of serrations on the seizing jaws, in an interval 

 between anterior fin and ventral ganglion, and in the presence 

 of more than 50 per cent of posterior fin in front of tail-septum. 

 Finally, it differs from 8. macrocephala in having a much shorter 

 tail, in the number of posterior teeth, and in the general form of 

 the body. 



Fowler (1906) suggested the possible synonymy of 8. elegans 

 and 8. zetesios (which has been identified by Ritter-Zahony 



