270 DISCOVERY REPORTS 



Hence i/oi = 13-5, and the difference, which indicates that the smallest individuals were found almost 

 entirely near the upper Hmits of the depth range of the species, is very strongly significant. From this 

 it appears that the summer migration of R. brachyurops on to the shelf is a breeding migration, 

 particularly when we remember that nearly all the very young specimens have been secured in the 

 autumn, when the movement towards shoal water of the species as a whole appears to be at its height. 

 The sex ratio of R. brachyurops seemed to be remarkably constant whatever grouping of the data 

 was adopted. For all specimens whose sex was recorded it worked out at 477% males. There are 

 indications that shoaling is more marked towards the end of the year, but large schools segregated 

 according to sex, such as are known to occur in some European species, were not encountered: 



Raja griseocauda Norman. Eight specimens of this new species were trawled : two at a deep northern 

 station, two at a deep intermediate station, and one at each of four southern stations, three of which 

 were in deep water and one on the shelf edge. Its distribution is much like that of R. scaphiops. It 

 seems to be one of a group of uncommon deep-water rays : R. doello-juradoi, R. scaphiops, R. griseocauda 

 and R. albomacidata, that occupy an ecological position in the Fatagonian fauna similar to that of 

 R. falsavela, R. hyperborea and R. oxyrhyticha to the north-west of the British Isles (Meek, 1916). 

 The scanty distributional data for R. griseocauda are shown in Fig. 9, and the depth records are sum- 

 marized along with those for the other species. None was taken in ' Other gear ' : 



WS218 



WS236 



IVS245 

 WS250 



WS817B I 



WS824 I 



Psammohatis extenta (Carman). A single specimen trawled at St. WS788B in the northern region 

 is assigned by Norman (1937, pp. 28-9) to this species. Previous records were mostly from the 

 Brazilian coast south of Rio de Janeiro, suggesting that the area we surveyed is south of the normal 

 range of the species. 



Psammobatis scobina (Philippi). Except Raja brachyurops, this was the most abundant elasmo- 

 branch we found during the trawling surveys. It was most definitely a species of the shelf, and was 

 found in fair numbers closer inshore than any of the other shallow-water rays. (The slightly shallower 

 'effective mean depth' of R. magellanica is not significant, and doubtless is due merely to insufficient 

 sampling of that less common species.) Psammobatis scobina was rare in the northern region and 

 relatively most abundant in the intermediate region, especially close inshore off Puerto Deseado and 

 Puerto san Julian. It was fairly plentiful in the southern region also, but was only twice recorded 



