432 PROP. 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 Berardiiis, the transverse processes are not perforated, but grooved pos- 

 teriorly. In the eighth of M. grai/i a vertical arterial canal passes through the base of 

 the rudimentary transverse process, which in the corresponding vertebra of M, australis 

 is grooved only ; in the ninth and all succeeding vertebrae of both skeletons the canals 

 pierce the sides of the bodies. 



Of chevron bones there are nine present in the skeleton of M. australis, and eight in 

 that of M. 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 laminse, 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 haemal spines are longer proportion- 

 ally than in Berardius, corresponding in this respect with the neural spines. 



The Sternum of the adult M. australis (Plate LXXIII. 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 M. grayi the sternum (Plate LXXIII. 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 M. australis. 

 Its length is 17 inches =432 millims., its greatest breadth 5"-7 = 145 milhms. 



The Bibs. — In the skeleton of 31. australis there are nine, in that of M. grayi tea 



