50 BULLETIN 73, UNITED STATES NATIONAL MUSEUM. 



seventh and eighth thoracic vertebrae are those on which the mode of attachment 

 of the ribs changes in ziphioid whales, and I have observed in the genus Mesoplodon, 

 as here, that the processes and articular facets were very variable, being sometimes 

 ' quite unlike on the two sides of the same vertebra. The direction of the acromion 

 is probably subject to large individual variations, though this can not be deter- 

 mined at present, and the same is true of the form of the first phalange of the first 

 digit. The form of the sternum is quite variable in all cetaceans, and can not be 

 relied on for specific characters, without comparison of many individuals. 



On the whole, I am of the ophiion, as already stated, that we are not compelled 

 by the differences noted to regard the Barnegat and Newport skeletons as repre- 

 senting different species. The Charleston skeleton is too young and imperfect to 

 admit of serious consideration. The idea that the differences between the adult 

 skeletons are probably individual receives support from the fact that the skeleton 

 shown in the photograph from St. Simon Island, Georgia, mentioned on page 31, 

 No. 14, appears to possess a combination of characters exhibited by the other two. 



AGE VARIATIONS IN SKULLS. 



The series of skulls of Z. grehnitzkii, which the Museum owes to the activities 

 of Dr. L. Stejneger and Mr. N. Grebnitzki, comprises specimens of different ages, 

 and, as will be shown presently, probably both sexes. Taken together with the 

 skulls from the east coast of the United States they probably represent very fully 

 the variations which the skull undergoes in the present species. These changes 

 may, perhaps, be best made evident by the following brief descriptions of the 

 various skulls : 



21975. Charleston, South Carolina. — Young female. (Type of Z. semi functus.) 

 All sutures open, and elements of occipital bone distinguishable. No meseth- 

 moid ossification. Opposite maxillary notches, premaxillte closely approximated, 

 nearly flat and horizontal, and about level with adjacent parts of maxillae. Left 

 premaxilla grooved longitudinally at this point. Orifice of anterior nares on a 

 level with lower end of rectangular projecting boss formed by superior portion of 

 nasals. Kostrum pointed, much broader distally than it is deep. A very distinct 

 rudimentary alveolar groove in distal end of each maxilla. Proximal end of vomer 

 resting against anterior face of nasals and reaching up to overhanging boss. Anterior 

 face of the latter nearly flat. (PI. 14, fig. 1 ; pi. 18, fig. 1 ; pi. 20, fig. 1 ; pi. 21, fig. 2.) 



Rami of mandible not anchylosed together at symphysis. Teeth hollow, 

 open at the root, gcute at apex, tipped with enamel; diameter 10 mm (PI 22, 

 fig. l;pl. 24, fig. 1.) 



30971. Barnegat City, New Jersey.— Adu\t female. Majority of sutures open, 

 but those on superior surface of rostrum between maxillas and premaxilla partly 

 anchylosed. Vomer nearly all anchylosed to rostral portion of premaxilla? ; it 

 presents a slight median elevation, but there is no mesirostral ossification. Right 

 premaxilla in front of nares broad, flat, and horizontal; left, nearly so, but with a 

 quite broad longitudinal groove. Opposite maxillary notches premaxillse nearly 

 on a level with adjacent parts. Orifice of anterior nares level with lower end of 

 nasal boss. End of rostrum quite acute, and broader than deep. Rudimentary 



