THE WHALEBONE WHALES OF THE WESTERN NORTH ATLANTIC. 



135 



Formulae for various American specimens are as follows : 



BALJENOPTERA PHYSALUS (L.). AMERICAN. VERTEBRAL FORMULA. 



These various formulae exhibit a considerable divergence, with no special line 

 of separation between the American and European specimens. As already re- 

 marked, several of the formulae require a certain amount of modification because 

 the specimens were somewhat defective, the number of ribs and chevron bones 

 actually present probably being less than the original number. These modifica- 

 tions will now be considered, and afterwards a revised table of formulae. 



RIBS. 



In skeletons of B. physalus which have been examined under favorable condi- 

 tions, it has been noted that the last pair of ribs is much shorter than the penultimate 

 pair and is not attached to the vertebral column. In other words, the last rib is 

 normally a " floating " rib. It has also been observed that the first chevron bone 

 is smaller than the second. These facts and other indications lead to the belief 

 that museum skeletons in which the last pair of ribs is as long as the preceding 

 pair and the first chevron as large, or nearly as large, as the second are defective in 

 these parts. Granting this assumption to be correct, we will consider the various 

 formulas in the preceding tables. 



Regarding the Vlieland Id. skeleton (1851) Flower remarks: "There are 14 

 pairs of ribs present; but as the 14th has not the characters usually met with in 

 the last rib, and as the 15th vertebra has the end of the transverse process thick- 

 ened and showing traces of an articular surface, it is most probable, as Van Beneden 

 supposes, that the 15th pair has been lost." {P. Z. S., 1864, p. 414). Flower also 

 remarks that though Van Beneden cites 14 or 15 as the correct number of lumbar 

 vertebrae " the place of attachment of the first chevron bone in the skeleton indicates 

 but 13 as belonging to this series." (Ibid., p. 414). The formula for this skeleton 

 with these corrections would be: 7, 15, 13, 27 = 62. 



1 The i4th pair of ribs is as long as the preceding ones, and hence an additional pair is 

 doubtless to be counted. 



' As the first chevron in position is of large size, it is probable that an anterior one is wanting. 

 The condition of the inferior carina of vertebra No. 36 indicates that such was the case. 



1 The isth pair of ribs is as long as the preceding pair, and hence 16 pairs may have been 

 present originally. * Fretal. 



