UlSTRIBUTION OF THE CHAETOGNATHA 205 



(c) Eukrohnia sp. 

 £. /ow/m Ritter-Zahony, 191 1 (part). 



This form, which was considered to be E. foivleri by Ritter-Zahony, appears on careful examination 

 to be a species in its own right. The number of teeth, the absence of eye pigment, and other points 

 separate it from E. foivleri. It will be described and named in a separate publication. 



Horizontal distribution. Circumpolar, northern limits not known, but it has not been found in 

 the Discovery collections north of the subtropical convergence. It is possible that it may be found in 

 other oceans, but it seems at present to be an endemic form. 



II. Species common to other regions 



{a) Sagitta maxima 

 Sagitta maxima (Conant) 1896. 



Spadella maxima Conant, 1896, Johns Hopkins Univ. Circ. 15, p. 84. 

 Sagitta whartoni Fowler, 1896. 

 S. gigantea Broch, 1906. 

 5. maxima Ritter-Zahony, 1911; Germain, 1913; Jameson, 1914; Huntsman, 1919; Burfield, 1930; Bollmann, 1934; 



Thiel, 1938 (part); Fraser, 1952. 

 5. lyra Michael, 191 1 (part). 



Doubts have been expressed about the validity of this species, notably by Michael (191 1, 1919) and 

 Thomson (1947), but it is in fact an easily recognizable form which can be differentiated from its 

 near relatives .S. lyra and S. gazellae by its greater tail-segment percentage, the position of the com- 

 mencement of the anterior fins, and the position of the seminal vesicles. 



The Southern Ocean form of this species is considerably smaller than its arctic counterpart (see 

 Plate X). The latter has been reported at more than 90 mm. in length (Fraser, 1952), whereas 55 mm. 

 appears to be the maximum length of the southern form. It can be seen from Plate X that the arctic 

 specimen is, apart from its much greater length, a far more massive creature than the southern 

 specimen. It seems quite possible that a careful study of these two forms would reveal, at the least, 

 sub-specific differences between them. 



Horizontal distribution. Circumpolar in the West Wind Drift, most abundant in the sub- 

 antarctic zone. It is apparently absent from the more tropical parts of the Indian Ocean, as it was not 

 found in the two series of stations in 90° E made between 30° S and the equator, where nets were fished 

 to 1 500 m. (stations 2683-91 and 2886-96). It occurs in the Benguela Current as far north as 22° 48 'S, 

 Station W.S. 976 (Station List 'William Scoresby ' 1950, 1953), and Thiel may have found it further 

 north in the Atlantic, though his records may well have been of S. lyra which he failed to distinguish 

 from S. maxima. In the Peru Current it occurs as far north as 04° 20-4' S, Stations W.S. 701 and 722, 

 though three of the specimens taken in this area were far from typical of either the arctic or antarctic 

 forms, resembling S. lyra in many features. Table i shows a comparison of the Peru Current specimens 

 with two subarctic specimens and a series from the Southern Ocean. Whereas the arctic and Southern 

 Ocean forms have very similar armature formulae at the same stage of maturity (though at very 

 different lengths), the Peru Current specimens show a very considerable reduction of head armature 

 with advancing maturity. It seems possible that a study of the Peru Current population of S. maxima 

 might shed considerable light on the phylogenetic relationships of the group of chaetognaths composed 

 of S. lyra, S. gazellae, and S. maxima. 



