382 DISCOVERY REPORTS 



somewhere— perhaps farther inshore, or ahogether to the north of our area— it is more common. 



Xystreurys also reaches ' pan-size '. 



Mancopsetta maculata (Giinther). A single specimen of this rare species was obtained during the 

 trawling surveys at St. WS218, in deep water over the edge of the shelf, just north of the southern 

 boundary of our northern region. It was 24 cm. long. Norman (1937, p. 136) refers to this specimen 

 as taken 'north of the Falkland -islands'. This is true, of course, but might well obscure the fact that 

 it was well over three hundred miles to the north of them. This capture off the Patagonian shelf is 

 interesting because the species was previously known only from the holotype collected by H.M.S. 

 ' Challenger' in 310 fm. (567 m.) off Prince Edward Island in the Indian Ocean. Although such wide 

 distribution is not unknown among more versatile pelagic fishes, such as Thyrsites, this is the only 

 example known to me in a group so specialized as the Heterosomata. E. R. Gunther noted 'it is 

 evidently a species inhabiting deep water and is unlikely to be of commercial value'. 



Achiropsetta tricholepis Norman. This genus was discovered during the investigations here described. 

 Two specimens are known. One, 10 cm. long, was taken at St. WS89 off Tierra del Fuego. It was 

 noted as 'having a grey colour, but highly transparent so that heavy print could be read through 

 most parts of the body'. In 1932 further hauls were made round the position of St. WS89 in hopes 

 of finding more, but none was taken. 



The other specimen had been found at the Falkland Islands some years previously, but was not 

 reported until the publication of Norman's paper in 1937 (p. 136). It was seen from the jetty in 

 Stanley Harbour swimming near the surface, and was caught in a bucket by Mr Bert Radclif. Dr J. E. 

 Hamilton into whose hands the specimen passed had independently noted the transparency of the 

 living fish. E. R. Gunther suggested that the transparency may be related to a surface swimming 

 habit, accounting for the virtual absence of the fish from our bottom nets, and its occurrence on both 

 sides of the Falkland trough : 



WS89 I, of 10 cm. in the trawl 



Port Stanley Pigzz i, of 10-5 cm. (J. E. H.) in a bucket at the surface 



FEATURES OF GENERAL BIOLOGICAL INTEREST 



To draw up a useful formal summary of a work of this kind would be difficult, and perhaps even 

 impracticable. It is a long report, but it is in itself little more than a collection of summaries, for it 

 deals only with the more important aspects of a body of data too vast to be analysed in full at present ; 

 and for some species the text is already compressed to only a few lines. The present section, however, 

 may serve a useful purpose in focusing attention on some of the features of general biological interest 

 that have emerged. These have already been discussed as fully as the data allow, in the notes on the 

 several species. First, however, I take the opportunity to repeat, in as near to summarized form as 

 possible, the essential features of the environment described in the introductory sections. These must 

 constantly be borne in mind if the other features are to be properly appreciated. 



The Patagonian Continental Shelf is the largest expanse of sea shallow enough to support a con- 

 siderable population of demersal fishes, in the cold temperate zone of the southern hemisphere. That 

 part of it which we surveyed, between 42 and 52° S lat., is rather larger than the North Sea. The main 

 physical features of this area are : 



(i) Uniformly moderate depths over the ' plain of the shelf with very slight depth gradient as one 

 proceeds offshore from the 80 m. to the 200 m. contour. Abrupt descent to oceanic depths ' over the 

 edge'. (This means that there is but a very small area below 200 m. accessible for trawling, despite 

 the great width of the shelf.) 



