44 



BULLETIN 73, UNITED STATES NATIONAL MUSEUM. 

 CHEVRONS. 



The number of chevrons in the North American and some other specimens is 

 as follows : 



The chevrons are similar in form in the three North American specimens, 

 with some differences whicli will be pointed out below. 



Neivport (male). — The lirst chevron consists of a pair of bones which are not 

 united. They are longer than deep, their depth indeed being less than that of 

 any one of the succeeding bones except the tenth and eleventh. Each pre- 

 sents one strong superior articulating facet. Second chevron, elongated antero- 

 posteriorly, but not much deeper than the first. Third chevron very deep and 

 only equaled in that respect Ijy the fourth ; narrowed and rounded off below. Fourth 

 chevron largest and broadest (antero-posteriorly) of the series; expanded below 

 and the lower border transverse. Fifth to eighth similar in form, but less deep 

 successively, and the lower border more rounded. Ninth similar to eighth, but 

 smaller and tliinner. Tenth similar to first, longer (antero-posteriorly) than deep. 

 Eleventh similar to tenth in form, but smaller. 



Barnegat f'Hy (female). — First chevron bone lacking. wSecond like that of 

 Newport skeleton, but smaller. Third similar to second, but much larger and 

 more produced posteriorly ; quite unlike the third in the Newport skeleton in form, 

 and much less deep. Fourth, largest and deepest of tlie series; anterior and pos- 

 terior borders rounded, and the inferim- border similar. Fifth to eighth similar in 

 form, but successively less deep, anil all more expanded below; inferior border 

 nearly straight. Ninth similar to eighth, but depth not exceeding breadth; lower 

 angles produced. 



Charleston (female, jr.). — The chevrons of this sj)ecimen resemble those of the 

 Newport skeleton, but on account of immaturity they are all more or less rounded. 

 The two sides of the fii'st chevron are united. The second is without the posterior 

 angular projection seen in the other specimens. The third is the deepest of the 

 series. The eighth is not deeper than long, and hence resembles the tenth chevron 

 of the Newport skeleton in proportion, but is, of course, much smaller. Two or 

 three chevrons are lacking from the posterior end of the series. 



Barnegat City (female). — First rib shortest and broadest, but considerably 

 broader at proximal end than at distal end. Head and tubercle close together. 

 The succeeding ribs increase in length and decrease in breadth to the fifth or sixth. 

 The third, fourth, and fifth are expanded and flattened at distal end. Seventh, 

 eighth, and ninth successively shorter. Distance between head and tubercle 



