A RARE PORPOISE OF THE SOUTH 

 ATLANTIC, PHOCAENA DIOPTRICA 



(LAHILLE, 1912) 



By J. E. Hamilton, D.Sc. 

 -QECORDS have been published of three specimens of Phocaena dioptrica, all from 



IV the South Atlantic region. ^ , r ^ u 



The type was described by LahiUe (1912) and was a pregnant and therefore adult 

 female caught near Quilmes on the River Plate. A second female was captured m the 

 Rio Santiago, and the third, a male, was taken at the same place about a year later. 



Two more may now be added to the list of known specimens; one, secured by Sir 

 Hubert Wilkins at South Georgia in 1923 durmg the Quest expedition and the other 

 from the Falkland Islands. The latter was brought to me by a shepherd, G. Butler, who 

 found it on the beach in a practically skeletonized condition. The sex could not be 

 determined and the lower jaw and flippers were missing. The length from the tip of the 

 snout to the notch of the flukes was 185-5 cm. Wilkins's animal was only 135-9 cm. 



EXTERNAL APPEARANCE 



Lahille describes, with photographs, his female and the foetus which it contained. 

 Bruch's paper is illustrated with photographs of both of his animals and there are de- 

 tailed notes on the Quest specimen to which I have had access by courtesy of Dr Eraser 

 of the British Museum (Natural History). , , , u , 



The colouring of P. dioptrica is striking and distinctive. In the aduk the back except 



for a broad band on each side of the upper jaw, is bright black. On the dorsal keel of 



the caudal region this colour disappears but reappears on the flukes where it extends 



over the emire dorsal surface. The remainder of the animal is clear white except that 



the ventral surface of the flukes has a grey border, and a few dark lines radiate frorn the 



caudal notch. A series of fine almost imperceptible grey lines form a faint wavy band 



extending from the lower jaw to the pectoral fin which is white, with pale grey edges. 



A black patch surrounds the eye, and in the type the latter was nearly surrounded by 



a narrow white line. From this white mark arose the comparison with a spectacled 



condition which suggested the specific name. • > 1 ^ 



In Bruch's male there seems to have been no spectacle mark and m Wilkins s also, 



an immature female, it appears to have been absent. My specimen was not in a condi- 



tion to allow any observations. •- ^- 1 „u 



The well-grown foetus from LahiUe's ammal shows colour markings identical with 



those of the adult except that the dark colour is carried along the dorsal keel of the tail, 



the mandibulo-pectoral band is very distinct, the white mark over the eye is reduced. 



