AND OTHER SPECIES OF CEPHALORHYNCHUS. 633 



parison of the skull with the other Falkland Is. specimen 

 confirms this conclusion. The only difference of importance is 

 that the rostrum of Mr. Yallentin's specimen (B) is distinctly 

 narrower at its base than is that of Mr, Hamilton's skull (A). 

 Flower (1883, p. 469) stated that the rostrum becomes longer 

 and wider, in proportion to the brain-case, in older Dolphins. 

 The skull B has an unfinished appearance in the region of the 

 base of the rostrum, as if growth were there incomplete ; and 

 the notches in the maxillee are wider than in A. The two skulls 

 are practically alike in their orbital width, and by an addition to 

 the rostrum at its base, B would become similar to A in the width 

 of this structure and in the reduction of the maxillary notches. 



C. eutropia and Philippi's three species alhiventris, platyr- 

 rhimis, and panope agree with one another in having a rostrum 

 which in length exceeds 50 per cent, of the total skull-length. 

 The tooth-row is also relatively long in the same species, the 

 percentage in C. eutropia (type) being 46*3, as shown by the 

 preceding table, and ranging from 46"0 to 51 "5, as shown by 

 Philippi's measurements, in the other three species. C. commer- 

 sonii agrees with G. Jieavisidei, and differs from the other four 

 species, in having a rostrum less than half the length of the 

 skull, and a shorter tooth-row, not exceeding 42 per cent, of the 

 skull-length. The skulls of the two species are also absolutely 

 smaller (29-30 cm.), C. eutropia having a skull more than 36 cm. 

 long, and those of Philippi's three species ranging from 33*0 to 

 39-5 cm. 



Although C. commerso7iii has a considerable resemblance to 

 C. heavisidei in cranial characters, I have noted the following 

 diff"erences in the skulls available for comparison (PI. II. figs. 2 

 & 3). The skull of C. heavisidei has previously been figured by 

 Schlegel and by Yan Beneden and Gervais, as pointed out below ; 

 and that of C coTiimersonii by Moreno (1892, pi. viii.). 



Premaxilla. — The outer edge of this bone, in Ceplialorhynchus 

 generally, forms a prominent elevated ridge in front of the 

 anterior nares (Flower, 1883, p. 473). In C. com^nersonii the 

 left bone is not prolonged behind this ridge, that of the right 

 side forming a slender splint passing towards the nasal of its 

 side, but not reaching it. Moreno's fig. 1 a seems to agree in 

 this respect. In C. heavisidei this posterior process is consider- 

 ably larger in the left premaxilla, and still larger in the right 

 bone, where it is 12 mm. wide and touches the nasal, passing 

 back to about the middle of its length. C. eutropia resembles 

 G. heavisidei in these respects, except that the right premaxilla 

 does not r-each the nasal, from which it is 11 mm. distant. The 

 floor of the depressed triangle in the premaxillse, in front of the 

 anterior nares, is flatter in G. commersonii than in G. heavisidei, 

 Avhere it is slightly concave. The width of the premaxillee in the 

 front half of the triangle is distinctly greater in G. heavisidei 

 than in the other species, and the maxillte are here corre- 

 spondingly narrower. 



