424 PROF, W. H. FLOWER ON THE GENUS MESOPLODON. 
The principal dimensions of these crania are as follows :— 



| M. australis, M, gray, | M. hectori, 
| adult. young. young. 
| inches. millim, inches. millim, inches. millim, 
Extreme length of cranium ...........-.. 30:3 770 30°3 1 770* 22:3 567 
| Length of rostrum (from the apex of the 
| preemaxilla to the middle of a line drawn | 
| between the anteorbital notches*) .... .. 19-9 505 202 | 510 12°6 320 
| From middle of hinder edge of palate (formed 
by the pterygoids) to apex of rostrum....| 23-8 605 245 | 622 17-4 442 
Greatest height of cranium from vertex to | 
| Splenvoodsactes sate. meetin te 11:0 27 10-4 | 264 9-5 241 
Breadth of cranium across middle of superior | 
Marini OMOnDits yy ci a scias ea cise naa 11:2 283 105 | 268 9-2 235 
Breadth of cranium between zygomatic pro- 
cesses Of squamosals .........002eeees INle7¢ 298 als: 282 10-2 259 
| Breadth between anteorbital notches ...... 7-4 187 7-2 183 53 135 
| Breadth of middle of rostrum ............ 17 44 1-6 40 15 37 
| Breadth of occipital condyles ............ 3:9 99 37 95 3°6 92 
| Premaxille, greatest width behind anterior 
TAOS eevee woh Ree aa ee ce Me een a oneal 54 138 51 138 4:6 117 
Praemaxille, least width opposite anterior 
MATOS ce tasvalere crores aieulaiecensensyste were ete 4-4 111 4-0 103 4:2 107 
| Premaxille, greatest width in front of an- 
PORE Ei Giaerehees | Sateen a DOC ctntS peck 46 117 44) 111 45 114 
| \Wadth of anterior nares) <..-....+.--+--- 2:70 | 52 21 | 53 2:0 51 
| Length of tympanic bone ................ 19 | 49 2:0 51 21 54 
| Greatest breadth of tympanic bone ........ 1:3 32 et) 85) 
Mandible, length of ramus .............. 26:0 | 660 19-1 484 
Mandible, length of symphysis............ 84 | 214 59 150 
Mandible, greatest vertical height of ramus, . 4-1 105 3:3 83 









The lower jaw appears to present no differentiating characters whereby the different 
species of MWesoplodon can be distinguished, except as regards the implantation of the 
teeth, which will be considered presently. 
The thyro- and basihyals are present in the younger skeleton but not in the older 
one. They are not united. In general form they resemble those of Berardius and the 
ordinary Dolphins, presenting none of the peculiar enlargement and flattening cha- 
racteristic of Physeter and Kogia and seen to a slight extent in Hyperoodon. The 
stylo-hyals are preserved in both skeletons, and, allowing for difference of age, are 
similar. ‘They do not present the simple cylindrical characters of the same bones of 
all the true Dolphins, and even of Physeter and Berardius, but are (especially those of 
the older specimen) remarkably flattened and widened towards the lower end, and thus 
approximate to the form which has hitherto been thought peculiar to Hyperoodon. 
In M. australis these bones have a length of 5"*6 = 142 millims., and a greatest 
‘ As the apex of the rostrum is stil] covered with the dried gum, this is not absolutely exact. 
* Thave thus defined the commencement of the rostrum for the sake of uniformity with previous measure- 
ments; but, owing to the breadth of the maxilla in front of the anteorbital notches, the rostrum in Mesoplodon 
appears to commence more than an inch in advance of the spot indicated. 
