634 SIR SIDNEY HARMEIl ON COMMERSOn's DOLPHIN 



Maxilla. — C. conimersonii seems to be characterized by the 

 specially large posterior expansions of the maxillae. Measuring 

 the length of these expansions from the bottom of the maxillary 

 notches along a line parallel with the middle line of the skull, 

 and the breadth as indicated in the table of measurements, these 

 parts are absolutely longer in C. conimersonii than in the con- 

 siderably larger type-skull of C. eutropia. In G. heavisidei they 

 are relatively narrow, and do not completely cover the orbit, the 

 whole upper margin of which is visible in a dorsal view, with 

 part of the postorbital process, which slopes a good deal 

 outwards. 



In C coinmersonii, the front of the orbit is completely con- 

 cealed by the maxillary expansions, the only part visible dorsally 

 being the postorbital process, which is more vertical than in the 

 other species. Rather more of the upper surface of the orbit is 

 shown in Moreno's figures, particulai-Iy in fig. 2, which is 

 described as representing a younger specimen ; and the extent of 

 the overgrowth of the orbit by the maxilla is perhaps dependent 

 on age. 



In G. heavisidei there is a slight constriction of the outer 

 margin of the rostrum, 20 mm. in front of the maxillary notches, 

 so that a small lateral lobe is partially marked ofl' at the base of 

 the rostrum, on each side. These lobes do not occur in 

 G. commersonii. 



Nasal. — These bones, though no donbt variable, show certain 

 features which may be distinctive. In G. heavisidei they are 

 subdiscoidal, the central part the thickest and the margin thinner, 

 and they are in contact with one another, on the upper side only, 

 for about 7 mm., leaving a small triangle of the frontals un- 

 covered between their lower borders and the mesethmoid. The 

 greatest diameter is 25 mm. In G. eutropia each bone is quite 

 twice as wide as long (25, 11 mm.), and has* a sharply marked, 

 nearly vertical, anterior face, which almost reaches the meseth- 

 moid. The left nasal is wanting in skull B of G. commersonii, 

 and the right nasals are not altogether alike in the two skulls. 

 The shape seems to be somewhat intei-mediate between those 

 of the other two species, being more quadrangular than in 

 G. heavisidei, and rather longer in proportion to the width than 

 in G. eutropia, the two bones having a median suture nearly 

 reaching the mesethmoid. The right nasal of skull A measures 

 22 mm. in width and 17 mm. in length, Morenos fig. la gives 

 similar evidence. 



Mandible (PI. III. fig. 2). — While differing in certain respects, 

 all three species show, more or less distinctly, the outwardly bowed 

 rami, corresponding with the expanded part of the rostrum, 

 given by True (1889, p. 108) as a generic character. That of 

 G. eutropia (c) is much larger and heavier than those of the other 

 species, but it resembles the mandible of G. commersonii (b) in 

 general form and in the shape of its coronoid process, which is a 

 blunt triangle with its apex directed nearly vertically and lyino- 



