982 MR A. PRINGLE JAMESON ON THE 



more accurate to omit this altogether, and indeed it seems to be the custom of many 

 investiijators not to include this fin in their measurements. 



As alcohol was the fluid in which the specimens were usually preserved, the identi- 

 fication has in many cases been attended by some considerable difficulty, for, as is 

 now well known, the only successful method of preserving Chsetognatha is by using 

 formalin, as alcohol causes these animals to shrink very greatly and become opaque.* 



Sagitta hexaptera (d'Orbigny). 



This very well-marked species was taken at fifteen stations in the warmer Atlantic 

 waters. It seems to be undoubtedly a tropical and sub- tropical species, as pointed out 

 by Ritter-Zahony (19 Ll), no specimens occurring in the Antarctic collections. 

 Probably the forms of this species reported from the Antarctic are to be referred in 

 great part to the somewhat nearly related species S. gazelle. 



Horizontal distribution : 22° 19' N., 22° 07' W.-15° 54' S., 4° 59' W. 



Vertical distribution : surface. 



Temperature range : 72-2°-80-5° F. 



Stations: 12, 13, 14, 17, 19, 36, 54, 56, 59, 60, 62, 69, 498, 501. 



Sagitta gazellse (Eitter-Zahony). 



This was the most abundant Antarctic form found ; over a dozen easily identified 

 specimens were got, and a considerable number of fragmentary or badly distorted forms 

 are probably to be referred to this species. 



It seems somewhat strange that this species, which is well marked and apparently 

 abundant, should have been recorded so rarely. The species was first established by 

 Ritter-Zahony in 1909 from the material of the Gazelle expedition, and it was also 

 found very abundantly in the collections made by the German South Polar Expedition 

 (1901-1903). Some of the forms described by Fowler (1907) as S. hexaptera, from 

 the material of the British Antarctic Expedition (1901-1904), and others unnamed, 

 from New Zealand (Fowler, 1908), have been assigned to this species by Ritter- 

 Zahony (1911). 



The most characteristic features of this species are undoubtedly those which sufier 

 most in preservation. Among the smaller forms the tail-percentage and the number of 

 teeth and jaws are sometimes very similar to those of young S. hexaptera, consequently 

 immature specimens of the two species are very likely to be confused. With larger 

 forms these features become extremely characteristic for both species, and all likelihood 

 of confusion disappears. The diagnostic features which seem to be of most assistance 

 in identifying the species are the following : — The tail-percentage is characteristically 

 low, about 12-14 per cent, for the larger specimens; the anterior fin is comparatively 



* Alcohol was Ti.sed as a preserving mediniu on account of its suitability over formalin for the majority of 

 organisms in the plankton. — W. S. B. 



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