R.-J. ANDERSON. — CETACEA 709 
mer) to the length of Mesoplodon Hectori Gray. One small Mesoplodon 
Hectori, was rather longer than the smaller one of M. Layarp. The beak 
of the adult Mesoplodon Layardi, was very much larger than that of 
the young specimen (twice the Size). The mesorostral bone was fused 
to the premaxillæ, near their tips in the adult, so that it was not possible 
to indicate the amount of the beak apex that was formed by the prema- 
xillæ. The premaxillæ formed the beak in the young specimen. I give 
the condition with the premaxillæ and mesorostral bone united in Aeso- 
plodon Hectori. In Mesoplodon Layardi (juv) an elongated mesorostral 
furrow was seen and a bar of cartilage, in this furrow, which disappeared 
after maceration, the eburnated bone takes its place afterwards, but no 
mesorostral bone seems to exist in the young. The growth of this bone 
is associated with elongation of the beak, this bone becomes fused with 
the vomer, the maxillæ are more spongy. The surface of section through 
the beak is compared to a heraldie lozenge, the inferior angle of which 
was rounded. The vomer appears between the pterygoids. In HMesoplo- 
don Layardi the two pterygoids articulated with each other mesially for 
10°*,2 from the base of each plate in the adult skull, but these diverged 
and allowed first the vomer, and then the two superior maxillaries, to 
appear between them. In the younger skull the mesial articulation, 
between the two pterygoids was more complete, for the pterygoid inter- 
vened at the anterior part. (TurNer. Report on Cetacea of Challenger). 
The extracted tooth in Mesoplodon Layardi presented an alveolar end 
that was jagged at the border and closed. The length of the extracted 
tooth was 35,8, 16,5 of which had been included in the alveolus. In 
Mesoplodon Hectori the teeth were short, conical, and concealed bencath 
the mucous membrane. The pulp cavity existed beneath the proximal 
end of each small tusk—like tooth. Enamel, dentine and cement were 
found in the teeth of Layardi. Sections of the teeth of Hecror's 
Mesoplodon were not examined. In the quotation given by Prof. TuRNER 
it will be seen that the teeth are referred to as tusks. A figure of the jaw 
is given by the courtesy of Prof. Werpox of the Oxford University Mu- 
seum. Sir W. Turxer described the teeth in the Challenger Rep. 
In giving an estimate of the value of the parietal when comparing 
Mammalian groups it may be well to mention that Meckez who examined 
several fœtal skulls says that the condition usual prevailed in the fœtal 
Dolphin, a fœtal Narwhal and a fœtal Whale and the parietals are sepa- 
rated by the interparietal where the former bones approximate. The pa- 
rietals in the Elephant resemble apparently those of the fœtal Cetacea 
rather than those of the adult, and comparison of the bones in Plata- 
rista With-the parietals in a young Elephant is suggestive'. The points 
l'Kmause’s Festschrift. Internat. Monatssch., Band XXI. 
