No. 553] DISTRIBUTION OF THE CH2ETO GNA THA 



11 columns" and then writing the names of the species, 

 having those in question in each square made by the 

 intersecting " arrays." Such an arrangement is given 

 below : 









Body trans- 



ESP 1 — 









IS !£T 



aS£- 



IMS. 











& fir 







fSSrl 



An examination of this table shows that in every 

 square where S. bipunctata occurs there also S. decipiens 

 is found, and the same relation holds between S. ne- 

 glecta and S. regularis. These four species, then, are to 

 be regarded as constituting two very closely related 

 "couplets." A third " couplet," whose constituent 

 species are somewhat less closely related, is that of S. 

 ferox and 8. planktonis, which only differ in the propor- 

 tional extent of the posterior fin in front of the tail- 

 septum. The remaining species are clearly distinct. 



Turning attention to those Sagitta devoid of the col- 

 larette, S. enflata, S. hexaptera, S. lyra, S. gazelles and 

 S. bedoti are exceedingly transparent, while S. serrato- 



