206 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



and lowland localities have an equal chance of having dark or light 

 color patterns and should occur in both areas at random. Possibly, 

 then, other factors such as difference in moisture conditions, tempera- 

 ture, differences between a highland and lowland flora, and various 

 other ecological factors are playing a role. The highland set of 

 external factors may be favorable to white color patterns, while the 

 lowland ones favor the survival of dark patterns. 



These data indicate that subspeciation within the species A. apex- 

 fulva is due both to the effects of random variation in partly isolated 

 populations and to selective factors in the environment. 



SUMMARY 



1. The various forms of A. apexfiilva are organized into subspecies. 

 New subspecies to the number of 43 are recognized from a total of 

 78 forms. 



HORIZONTAL VARIATION 



2. The embryonic whorls may be either bicolored or unicolored. 

 Shells with bicolored embryonic whorls occur in regions I, III, and 

 Illb ; those with unicolored ones occur in regions II and IV. Regions 

 la, Ila, and Illa have embryonic whorls which are intermediate be- 

 tween the bicolored and the unicolored condition. 



3. The color pattern of the postembryonic whorls shows marked 

 differentiation between regions I, II, III, and IV, and less variation 

 within each region. More horizontal differentiation occurs in zone II 

 than in zone III. No horizontal migration is noted of one form 

 invading the territory of another, because A. apexfulva, like A. niuste- 

 lina (Welch, 1938), tends to break up into subspecies at different 

 elevations and at short distances away from a given colony. 



4. Highland forms occurring in zone III show as much horizontal 

 size variation as lowland forms in zone II. Half the ridge complexes 

 in zone II have 18+ shells, 22 percent have 19+ shells, and 27 percent 

 have a mixture of 18-I-, 17 -f, and 16+ , shells. In zone HI 22 

 percent of the ridge complexes have 18+ or iy+ shells, while 78 

 percent have 19 + , 20-I-, or 21 + shells. 



VERTICAL VARIATION 



5. Vertical variation occurs in the color of the embryonic whorls 

 between regions Ilia and III, and between regions IV and Illb. 

 Regions III and Illb have shells with bicolored embryonic whorls. 



