334 REPORT OF NATIONAL MUSEUM, 1884. 



that there was a large square area of soiled white on the abdomen and 

 numerous gray spots on the head. The coloration of the female monk 

 seal described by Cuvier (I. c.) approximates more closely to the speci- 

 men before us. The under surfaces of the former were yellowish light 

 gray, while our specimen is of a yellowish umber-brown color in the 

 same region. 



Much more important differences are found in the skull. In the Osse- 

 mens fossiles (vol. viii, 1836, p. 442-443), Cuvier gives a table of measure- 

 ments of the head and other parts of the skeleton of a specimen of M. 

 albiventer. Although Ouvier's specimen was larger than that under 

 consideration, the differences are such as, in our opinion, could not be 

 entirely due to disparity of age or difference of sex. The width of the 

 zygomatic arch in the former is much the greater, being about three- 

 fourths the length of the skull; in M. tropicalis its width is only three- 

 fifths the same length. This character is shown also in the close ap- 

 proximation of the coronoid processes and condyles in M . tropicalis. 

 While the length of the muzzle compared with that of the brain-case 

 is practically equal in the two species, its widtn is considerably less 

 in M. tropicalis than in M. albiventer. Both the measurements and 

 figures of. the latter species show that it has the forehead much more 

 elevated, and consequently the anterior nasal opening more nearly 

 vertical, than is the case in M. tropicalis. The foramen magnum 

 would appear to be twice as large relatively in M. tropicalis as in M. 

 albiventer. This character is perhaps of little value, on account of the 

 great variability observable auioug different individuals. 



A character which is apparently of great importance is the difference 

 in the relative length of the molar series. In M. tropicalis the length 

 of the molar series of each jaw is very nearly one-third that of the skull, 

 while in the Mediterranean seal it is less than a fourth. The condyle 

 of the mandible in M. tropicalis is noticeably low, being on a level with 

 the alveolar border of the jaw. On account of this disposition of parts 

 the lower edge of the occipital condyles is in the same plane with the 

 lower margin of the mandible when the mouth is closed. There ap- 

 pears to be no approach to this arrangement of parts in any other ear- 

 less seal. 



It is stated both by F. Cuvier and by Keyserling and Blasius (Fauna 

 Deutschland, 1857, p. 245) that in M. albiventer the first upper molar 

 is the smallest of the series. In M. tropicalis this tooth is considerably 

 larger than the fifth. 



Cuvier has figured the skull of M, albiventer with a prominent supra- 

 orbital tubercle, a process which is entirely rudimentary in our specimen 

 of M. tropicalis. 



In our opinion the differences pointed out are quite sufficient to 

 warrant the separation specifically of the subtropical seals of the 

 Eastern and Western Atlantic. It is decidedly probable that fresh 

 specimens of equal size and age from the two regions would show dif- 



