208 



DISCOVERY REPORTS 



(a) Sagitta hexaptera (d'Orbigny) 



A widespread species in subtropical and tropical seas with a considerable tolerance for the colder 

 parts of those areas; mainly an inhabitant of the surface lOO m. 



{h) Sagitta lyra (Krohn) 



A widespread species in subtropical and tropical seas, having a slightly greater tolerance than 

 S. hexaptera to cold water. Normally an inhabitant of the water layers below loo m. though infrequent 

 below 500 m. 



(c) Sagitta decipiens (Fowler) 



A widely distributed form typical of the water layers below 100 m. in the tropics and subtropics. 



Table 2. Length and head armature of all specimens of H. mirabilis so far reported 



(d) Sagitta minima (Conant) 



The distribution of this species is not at all well known, but it is common in the subtropics of the 

 southern hemisphere. 



{e) Sagitta serratodentata Krohn 



A very widely distributed form which exhibits considerable, possibly specific, variation. The most 

 cold-tolerant of the exotic species considered here, it normally inhabits the surface water. 



(/) Sagitta zetesios Fowler. 



An inhabitant of deep water, usually below 750 m., in tropical and subtropical waters. 



{g) Krohnitta siibtilis (Grassi) 



This is a common subtropical species usually in the 250-100 m. layer, but it is occasionally found 

 in surface hauls. 



[h) Pterosagitta draco (Krohn) 



A common surface form in warm latitudes. 



None of these species is common in the Southern Ocean, but all have been found, usually as single 

 specimens but occasionally as several together, at some time in the Discovery collections made south 

 of the subtropical convergence. None of these species has been found in Discovery collections made 

 south of the antarctic convergence, and usually they are not found more than two or three degrees 

 south of the subtropical convergence. Previous authors have recorded some of them in the Antarctic 



