Ko. 484] 



DISTRIBUTION OF CH.ETOGNATHS 



243 



It is the purpose of the present note to call attention to the 

 important contributions which investigators of pelagic h'fe might 

 make to the discussion of this phase of the prol)lenis of evohition 

 especially since monographers of pelagic groups are best qualified 

 to judge of the degrees of affinity between the species of the genus 

 and can determine whether the most closely related ones have a 

 coincident or contiguous distribution. It is exceedingly desirable 

 that future expeditions investigating the life of the high seas be 

 equipped for a fuller analysis of the details of vertical distribution 

 and that data on breeding seasons of pelagic species be included 

 in monographs whenever available. 



Genus Krohnia 



This genus includes three species, K. hamata, K. siibtilis, and 

 A', pacifica. The first are two oceanic species of wide distribution, 

 the last an Indo-Austral species of surface neritic distribution. 

 The horizontal area of distribution of the first two species is largely 

 coincident, A', hamata being known to extend to higher latitudes 

 (81° N., 52° S.) than A. subtllis (Oif X., 2\)° S.). As might be 

 expected from its temperature relations, A', hamata is recorded 

 from lower levels in the tropics than is A. .suhtllis. Data on this 

 point are not very complete as K. suf^fllis is not an abundant 

 species. The closing net catches of the Plankton Expedition 

 indicate a maximum depth of 1500 m. for A. hamata and S5() m. 

 for A', subtilis. The two occur together between 300 and 500 m. 

 (37° N). The extent to which the vertical distribution of the 

 two species overlaps cannot be deterniined from tlie available 

 data. Fowler (:05) shows that tlie size of the individual of A. 

 hamata increases with the depth in the Biscayan region. The 



and large ones with occasional small ones 1h>I.uv that level. The 

 sexual conditicm at different levels was not noted. The |)()ssil)ility 

 of overlapping distribution is certainly present l)ui contiguous 

 distribution is by no means e.\( lude<l. 



Krohnia hamata is foinid in the mesoplaiikton of the Indo- 

 Austral region, where A', pacifica is also found, but in surface 

 waters exclusively. These two sj)ecies were thus contiguous 



