l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



Telescoping with excessively dominant occipital thrust is seen in 

 the genera Balccna, Eiibalccna and Ncohalccna. A diagram showing 

 the general relationships of the bones at the vertex is given in figure i 

 of plate 8. It is taken from the photograph of a skull of Euhalmia, 

 but it will answer sufficiently Avell for the plan of all three/ The 

 occipital shield will be seen to have extended forward to a level dis- 

 tinctly anterior to the orbits and to the articular level of the squa- 

 mosals, completely excluding the parietal from the dorsal surface 

 of the skull, and reducing the median dorsal exposure of the frontal 

 to a narrow transverse strip of bone ; the nasal and nasal branch of 

 the premaxillary lie entirely in front of the orbit and of all of the 

 frontal except its unimportant median angle or projection. The 

 nasals and nasal branches of the premaxillary are thus situated 

 obviously in the rostrum with their posterior margins well in advance 

 of the orbital level ; and the base of the rostrum has no appearance of 

 having been pushed back against or into the structures which lie 

 behind it. A transverse line drawn across the dorsal aspect of the 

 skull through the base of the nasal will traverse also the pre- 

 maxillary and maxillary but no part of the frontal other than the 

 unimportant median projection (this projection is most strongly de- 

 veloped in Balccna). Such a relationship of the parts in the base of 

 the rostrum presents no' very unusual features as compared with the 

 conditions existing in ordinary land mammals. A slight lengthening 

 of the nasal branch of the premaxillary would bring it about in dogs 

 or cats or various ungulates ; it is almost realized in some of the 

 bg ars and pinnipeds, and it may be seen exactly reproduced so far as 

 essential features are concerned, in squirrels, pocket gophers and 

 other rodents (pi. 8, fig. 8). The side view of such a cetacean skull 

 (pi. 6, fig. 4) shows even more clearly how the post-rostral portion 

 has been overridden by the occipital shield while the rostrum has not 

 interlocked with the structures behind it. The intermaxillary has 

 extended backward to the same level as the base of the maxillary; 

 but neither of these bones shows any tendency to encroach upon 

 the frontal. On the contrary the forward push of the occipital region 

 seems to^ have crushed the frontal broadly against the maxillary, 



^ In the case of Ncohalccna, the skull of which I have not seen, I have based 

 my comparison of the conditions existing in the region of the vertex on the 

 figures published by Hector (Trans, and Proc. New Zealand Inst, Vol. 2, 

 pi. 2B, 1869) and Oliver (Proc. Zool. Soc London, 1922, Oliver, pi. i, Sep- 

 tember, 1922). They appear to have been made from a better point of view 

 than the one published by Beddard (Trans. Zool. Soc. London, Vol. 16, pi. 8, 

 1901). 



