452 PROF. W. H. FLOWER ON THE GENUS MESOPLODON. 
of the tail. As before mentioned, the appearance and size of the last vertebra present 
leads to the belief that in both cases an additional minute terminal vertebra has 
been lost. 
The arches and spines gradually diminish from the first, the last being on the eleventh 
in both skeletons; and in both the last trace of a transverse process is seen on the 
ninth. As in Berardius, the transverse processes are not perforated, but grooved pos- 
teriorly. In the eighth of JZ. grayi a vertical arterial canal passes through the base of 
the rudimentary transverse process, which in the corresponding vertebra of MW. australis 
is grooved only; in the ninth and all succeeding vertebre of both skeletons the canals 
pierce the sides of the bodies. 
Of chevron bones there are nine present in the skeleton of MV. australis, and eight in 
that of WM. grayi. These evidently correspond, the ninth being absent in the latter. 
The first (probably in reality the second) is small, and with the apex directed forwards. 
It consists of two lamine, united in the middle line below, but not developing a keel. The 
next has a considerable keel. The third is the largest, and in the adult skeleton has a 
flattened rough surface at the apex. ‘The fourth has a shorter but broader keel; and 
from this they gradually diminish to the end. The hemal spines are longer proportion- 
ally than in Berardius, corresponding in this respect with the neural spines. 
The Sternwn of the adult MW. australis (Plate LX XIII. fig. 5) consists of four distinct 
segments, connected only by cartilage, and, as is usual in the Ziphioids, not completely 
ossified in the middle line, so that a notch is left at the anterior and posterior end of 
each, forming a series of median foramina in the complete sternum. That between the 
third and fourth, however, is very small; that between the second and third is largest. 
At the anterior extremity two processes, projecting forwards, curve inwards, and nearly 
enclose another fenestra. The articular surfaces for the costal cartilages are well 
marked. The first is on the side of the first segment; the second between the first 
and second segment; the third between the second and third; the fourth between 
the third and fourth; the fifth on the side of the fourth segment. The terminal 
piece is unsymmetrical, being longer on the right than on the left side. The extreme 
length of the ossified sternum is 20 inches (508 millims.); the greatest breadth across 
the first segment is 5°8 inches (148 millims.). 
In WV. grayi the sternum (Plate LX XIII. fig. 2) presents all the characters of imma- 
turity, the anterior and other processes being completely undeveloped. Otherwise it is 
of much the same form as the former; but the part corresponding to the fourth 
segment of that one is larger, and separated into two by a transverse suture, of which 
but slight indications are to be seen at the same place in the sternum of VW. australis. 
Its length is 17 inches =432 millims., its greatest breadth 5’-"7=145 millims. 
The Ribs.—In the skeleton of M. australis there are nine, in that of WZ. grayi ten 
