PHOCAENA DIOPTRICA 



233 



lateral view as they are in P. phocaena. The upper surface of the rostrum is rather 

 abruptly rounded off in the last two centimetres in P. dioptrica (Plate V, figs, i, 2). 



In the ventral aspect the vomer of the adult P. dioptrica where applied to the pre- 

 sphenoid has broad lateral and posterior wings with a wide V-shaped depression be- 

 tween them posteriorly. The vomer also takes part in the formation of the posterior 

 edge of the palate in P. dioptrica but does not in P. phocaena (Plate V, figs. 3, 4). The 

 palato-maxillary suture of the former is deeply concave towards the front instead of 



Table II. Skull measurements 



The posterior part of the palate of Wilkins's specimen is damaged. 



being very shallow as in P. phocaena, and in the latter it is much more serrated. The 

 posterior part of the palate is damaged in the immature P. dioptrica and the curvature 

 of the maxillo-palatine suture is shallow. In both examples of P. dioptrica the maxillary 

 part of the palate is quite definitely convex from side to side and the condition is even 

 more pronounced in the iinmature specimen. In P. phocaena the corresponding part is 

 flattened or even somewhat excavated. 



In P. dioptrica the zygomatic arches are almost entirely concealed by the frontals, but 

 in P. phocaena they are so arched horizontally as to be easily visible from above. 



REFERENCES 



Allen, G. M., 1925. Burmeister's porpoise (Phocaena spinipinnis). Bull. Mus. Comp. Zool. Harvard, 



Lxvii, no. 5, p. 25. 

 Bruch, C, 1916. El macho de Phocaena dioptrica Lah. Physis, Buenos Aires, 11, no. 12. 

 Lahille, F., 1912. Nota preliminar sabre una neuva espece de marsopa del rio de la Plata. Ann. Mus. Nac, 



Buenos Aires, xxiii, p. 269. 

 Wilkins, G. H., 1922. Shackleton-Rowett Expedition, Mammalogical Report. MS. in British Museum 



(Natural History). 



