234 - MK. n. o. roKBES o^^ the [Feb. 28, 



inch wide (measured on the upper surface). In the older specimen 

 (F) in the Otago Museum the maxillary ceases at 7*65 inches, 

 and in the type (K) at 9^ inches from the apex of the rostrum, 

 so that the groove practically ceases there. The lower flange 

 of this groove is generally traceable on the side of the rostrum 

 much more clearly than the upper, and in older specimens is very 

 pronounced at the base of the rostrum, decreasing in prominence 

 as it runs forward, especially in the Kaiapoi specimen (I) and in 

 31. australis, Flower. The depth of the groove and of its subtu- 

 bercular pit, and the divergence of its flanges, appear to vary with 

 age and sex, and would seem to be dependent on the individual 

 growth of the bones in the neighbourhood, especially the increase 

 forward of the palatines and pterygoids. In those forms in which 

 the buttress is strongly developed, a shallow depression or groove 

 separates the lower flange from the maxillo-pterygoid swelling. 



Seen from the palatal surface. 



From this aspect the relations of the palatine and pterygoid bones 

 in the two Otago Museum specimens (A, F), in the three Canterbury 

 Museum examples (H, I, K), and in M. f/rai/i of Flower's paper 

 in the Society's Transactions are identically the same. The pala- 

 tines lie on the outside of the pterygoids, reaching forward as far 

 as but not extending beyond their pointed ends; the pterygoids, 

 therefore, articulate directly with the uiaxillaries. In the M.(OhIo- 

 dou) grayi figured by Van Beneden the palatine bones completely 

 eurround the anterior ends of the pterygoids and extend anteriorly 

 to them, preventing their coming into contact with the maxillaries. 

 The same differences exist between the specimen in the Canterbury 

 Museum of Ziphius cavirostris, in which the palatine bones sur- 

 round the pterygoids, and the figure on plate xxi. his in the 

 ' Osteographie ' of Van Beneden, in which they do not. The same 

 dift'erences were also pointed out above in my remarks on specimens 

 of M. la>/ardi, and are therefore due solely to individual variation. 



The relations of the premaxillaries, maxillaries, and vomer on 

 this aspect of the cranium are the same in all these specimens, 

 the amount which each contributes varying with the age, sex, or 

 individual. 



The number of teeth in the gum of the upper jaw in the examples 

 I macerated, in one case exceeded by one, in the second case was 

 less by one, and in the third equalled that given by Sir Julius von 

 Haast in describing the type species. 



The triangular pterygoid in all these examples has the usual 

 everted lower border and deep fossa, as also the deep notch at the 

 base of the pterygoid plate, and presents no essential feature by 

 which the species can be separated one from another. The pterygoid 

 fossae in the three specimens I dissected contained each a large 

 air-sac opening into the ear-cavity, and communicating with the 

 mouth by the Eustachian passage. In M. gratji the pterygoid fossa 

 never extends anterior to the level of the maxillary tubercle. 



