INIA GEOFFKENSIS AND PONTOPOEIA BLAINVILLII. 103 



ally diminishing in size. The mode of attachment of the ribs to the vertebral column 

 has been noticed in the description of the thoracic vertebrse. 



The extreme length of the ribs of the right side in a straight line is as follows : — 



First 3-7 Eighth 6-9 



Second 57 Ninth 6-7 



Third 6-9 Tenth 6-5 



Fourth 7-3 Eleventh 6-4 



Fifth 7-3 Twelfth 5-9 



Sixth 7-2 Thirteenth 5-3 



Seventh 7'1 



The costal cartilages, as in Platanista and all the Physeteridae, are not ossified. How 

 many may have reached the sternum it is, in the present state of the skeleton, impos- 

 sible to determine ; but indications of the attachment of only two pairs are to be seen 

 on this bone, which, if confirmed, would be most exceptional among Cetacea, and be 

 another feature of resemblance with the Sirenia. 



The sternum (PI. XXVII. figs. 3, 4 & 5) is very peculiar in shape, quite unlike that 

 of any other Cetacean with which I am acquainted, and in its shortness, breadth, and the 

 deep notch on the anterior border somewhat recalling that of the Manatee. It differs 

 from this, however, in its gi-eater solidity, especially towards the anterior part, and in 

 possessing two strong triangular processes [h) projecting downwards and outwards from 

 the fore part of the external surface. 



It consists of a single bone, which is at present but incompletely developed, all the 

 prominences and the whole hinder margin terminating in cartilage. 



The extreme length of the ossified portion of this singular bone is 4"'2 ; its greatest 

 breadth, near the middle, is 3". Its general form is irregularly oval. In the anterior 

 border is a notch 1" in depth, with smooth, rounded edges. On each side of this are 

 two thick conical processes (a), projecting directly forwards, "7" apart at theii' ends. As 

 these have di-ied cartilage both on their tips and inner surfaces, it is possible that iu 

 the adult animal their ossification might extend so far as to convert the notch into a 

 foramen. On each side of the hiuder half of the notch the bone becomes very thick, 

 running out on the external or inferior surface into the triangular process before no- 

 ticed (5), and backwards and upwards into a thick irregular edge (c), apparently for 

 the attachment of the cartilage of the first rib. The hinder half of the bone is flat, 

 and gradually becomes thinner towards its rounded and incomplete posterior edge, wliich 

 is divided into two lobes by a narrow cleft, situated slightly to the right of the median 

 line. About the middle of the left lateral margin is a small transverse notch, re- 

 presented on the right side by an oblique perforation, apparently for the passage of a 

 blood-vessel. Immediately behind this the margin is thickened and excavated for the 

 attachment of the cartilage of the second pair of ribs {d). There are no other iudica- 



VOL. Tl. — PART III. Q 



