18 NORTH AMERICAN FAUNA 60. FISH AND WILDLIFE SERVICE 



In botli subgeiiora the plaiiti<ii-a(le structure of the feet is an out- 

 standing- feature. The fore feet somewhat resenihh' tiny hands, with 

 long lingers opposabk' to a liigli (k'gree, possessed of great strength, 

 and yet capable, in Procyon at least, of being used with a remarkable 

 deftness and delicacy of touch. The digits of the hind feet are much 

 less opposable, and the imprints of the l)r()ad flattened soles along 

 muddy shores may be liivened to those of a small child's feet. Al- 

 though the favorite haunts of the members of both subgenera are in 

 the vicinity of water and nnich time is spent upon the ground, Procyon, 

 as compared with Kuprocyoii, is provided with claws that are narrower, 

 sharper, more compressed laterally, and strengthened by greater ver- 

 tical depth at the base, better adapting this subgenus for climbing and 

 a more arboreal life. In Panama, where the two subgenera occur 

 together, the crab-eating habit is shared in common, but may be in- 

 dulged in to a greater extent by Euprocyon than by Procyon. The 

 broader, less trenchant cusps in the molariform teeth of Euprocyon, 

 as compared with those of Procyon, are better fitted for crushing hard 

 substances. Along the coast of Salvador, mangrove swamps are in- 

 habited by a local form, Procyon lotor dickeyi, which feeds extensively, 

 perhaps principally, upon crabs. The abrasive eft'ect of such a diet 

 on the teeth of a member of the typical subgenus is there strikingly 

 shown by the early wear and ra])id shearing off of the crowns of the 

 molars, leaving the premolars comparatively little aft'ected. In some 

 of the older specimens of dickeyi the molar crowns are reduced until a 

 mere shell remains near the roots. This may, however, be due to 

 some unusual local condition as such rapid or extensive wear has not 

 been observed anywhere else. 



The black mask varies somewhat in extent, and some forms are 

 paler than others, but owing to general uniformity in pattern of color- 

 ation in each subgenus, recourse must usually be had to size and to 

 cranial and dental modifications in tracing the relationships of species 

 and subspecies. 



In the subgenus Procyon most of the sutures of the skull are easily 

 traced at birth. Among the earliest sutures to close are those of the 

 basicranial segment surrounding the foramen magnum. The supra- 

 occipital, exoccipitals, and basioccipital are all firmly united, and the 

 sutures have disappeared before the permanent dentition' is fully in 

 place. The union between these bones and the remainder of the skull, 

 however, remains distinctly visible until finally closed later with ad- 

 vancing age. The jugals unite with the maxillae earlier than with 

 the squamosals. Progressive obliteration extends to the maxillo- 

 premaxillary sutures and to the median line between the frontals, 

 while the parietal sutures remain distinct. The closure of the parietal 

 sutures may be taken as an indication of maturity. In old age all the 



