74 BULLETIN 73, UNITED STATES NATIONAL MUSEUM. 



There are only ten thorack's in B. arnuxii, as already mentioned, but in B. 

 hairdii there are eleven, and the eleventh is that which bears the second transverse 

 process on the side of the centrum. 



The foregoing differences amount to this: That in B. hairdii the commencement 

 of the lower series of transverse processes is pushed back one vertebra, as com- 

 pared with B. arnuxii, and that in the ninth thoracic of the former species, which 

 corresponds to the eighth of the latter species, the metapophysis has a short process 

 on the side for the articulation of the tubercle of the rib, instead of merely a sessile 

 facet. Although in other genera of ziphioids these differences would perhaps be 

 looked upon as individual, since they are constant here they may be considered 

 specific, at least provisionally. 



SCAPULA. 



In B. hairdii the anterior border of the scapula is narrower than in B. arnuxii, 

 the anterior ridge coming close to it and lying parallel with it. The acromion is 

 directed more upward, so that the angle between it and the body of the scapula is 

 more acute, and the process itself is rather more expanded distally. The coronoid 

 is inclined a little more downward. The whole surface of the scapula is very 

 uneven. (PI. 33, fig. 2.) 



HUMERUS AND ULNA. 



The humerus is .shorter than in B. arnuxii and broader distally, and much more 

 recurved on the ulnar side. The ulna is much broader distally and its whole shape 

 is diflferent. (PI. 33, figs. 3 and 4.) 



CHEVRONS. 



As the skeleton of the typical form arnuxii has been described in considerable 

 detail and accurately figured by Flower and by "\'an Beneden and Gervais, it is 

 not considered necessary' to give a complete description of that of hairdii in this 

 place. The entire skeleton and many of the separate bones are figured in Pis. 

 42, 32, and 33. The phalanges are lacking altogether, or are incompletely repre- 

 sented, in the various skeletons of hairdii, and for that reason the phalangeal for- 

 mula can not be given. The chevrons number ten in the skeleton from Center- 

 ville beach, Cahfornia (Cat. No. 49725). Both Flower and Van Beneden and 

 Gervais give nine chevrons as the number for the skeleton of arnuxii in the Hun- 

 terian Museum, London, but the latter authors have added a tenth in outline in 

 the figure of the skeleton of that species which is in the Paris Museum. Ten are 

 mentioned by Hector as the correct number for the skeleton of ai'nuxii from Well- 

 ington Harbor examined by him.'^ 



STERNUM. 



Tlie sternum of hairdii (PI. 32, fig. 2) consists of five segments and does not 

 offer characters by which to distinguish it from that of arnuxii. In the former 

 species the first eight pairs of ribs possess distinct heads and tubercles; the tubercle 

 is rudimentary in the ninth pair and absent in the tenth and eleventh. 



The dimensions of the three skeletons of hairdii and of that of arnuxii described 

 bv Flower are as follows : 



"Trans. N. Z. Inst., vol. 10, 1878, p. 339. Hector remarks that in the skeleton studied by Flower 

 there were twelve caudals with facets for chevrons, but I do not find it so stated in the original account. 



