236 Sheppard : Xotes on the Skeleton of Sibbald 1 s Rorqual. 



of size in every direction, so marked that, if it did not occur in 

 both skeletons, one might easily suppose that a bone had been 

 lost from this region.' 



£ The principal peculiarity of the skull, which was pointed 

 out in the Utrecht specimen, was the breadth of the rostral 

 portion ; this is repeated, though to not quite the same extent, 

 in the Hull skeleton. The breadth across the middle of the 

 beak of the former is to the length of the skull as 27 to 100, in 

 the latter as 26 to 100. In six specimens of P. antiquorum it 

 varies between 18 and 21 to 100. The actual breadth (measured 

 across the upper surface following the curve) in the Hull 

 specimen is 33 inches, each maxillary being 10 inches and the 

 premaxillary 5 inches, the space between the latter 3 inches. 

 The nasal bones agree together, and differ from P. antiquorum 

 in being but slightly hollowed on their upper surface and 

 anterior margins. This character is most strongly marked in 

 the Hull specimen.' 



' The stylo-hyals are thicker, especially near the lower end, 

 in both the Utrecht and Hull skeletons than in the common 

 Fin-Whale.' 



'The sternum, which is so remarkable in the Utrecht speci- 

 men for its almost rudimentary state, is, unfortunately, wanting 

 in the Hull skeleton ; but even this absence may not be without 

 significance, for if it had been a large, well-developed bone, it 

 is most unlikely that it should have been lost in a skeleton 

 prepared with such care as to be in every other respect perfect.' 



' In the Utrecht skeleton (not articulated) there appear to be 

 but fifteen pairs ; while in that at Hull there are sixteen, the 

 last well developed — as long, in fact, as those which precede it. 

 If one could be certain that one had not been lost in the former 

 case, this difference might be of some importance ; but in 

 different specimens of P. antiquorum the last rib is in some 

 completely developed, and in others represented by a mere splint 

 of bone totally unconnected with the vertebral column, and 

 therefore easily overlooked in preparing the skeleton. If six- 

 teen is the normal number of the pairs of ribs in P. sibbaldii, 

 this makes a good specific distinction from P. antiquorum, which 

 has never been known to have more than fifteen. The first rib 

 agrees in both specimens, and differs in P. antiquorum in want- 

 ing a well-developed capitular process. In the Utrecht specimen 

 this process is present in the second, third, and fourth ribs — 

 longest in the third. In the Hull skeleton it is found from the 

 second to the sixth, being longest in the third and fourth. In 



Naturalist, 



