204 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



2. FORM 



A considerable amount of trouble has been taken to show the range 

 of form variation within each area. The extreme narrow and obese 

 forms of the shell are generally figured for each form and the measure- 

 ments given in the text. For example, various forms of A. a. turgida 

 have been figured on plate 6. The extreme obese form of the shell 

 (pi. 6, fig. 4a) looks very different from the narrow form of the 

 shell. The spire may be concave in outline (pi. 6, fig. 4^) or straight 

 in outline (pi. 6, fig. 5). The contrast between the narrow (pi. 5, 

 fig. 17) and the obese form (pi. 5, fig. 17a) of A. a. hruneola is 

 enough to lead to the consideration of the specimens, disregarding 

 color, as two different forms. In Hke manner specimens of A. a. 

 parvicolor (pi. 6, figs. 15, 15a) also show marked variation, as do 

 many other subspecies. Just as with color pattern, the shape and size 

 of the shell cannot be used as a criterion in determining a species, 

 unless a series of forms are available so that something is known 

 about the range of variation. 



D. Size Variation in the Same Colony over a Period of Years 



There is little information on this question. A. a. rubidipicta (area 

 II, ridge complex 3) collected from 1921 to 1929 shows little varia- 

 tion over a period of years (see table 2, p. 15). A. a. turgida (area 35, 

 ridge complex 8) collected from locality 202b from 1920 to 1934 

 shows no variation in the mean length of the shell over a period of 

 14 years. However, a lot collected in 1913 (table 2) is smaller than 

 the lots collected in 1920 to 1934. This difference in size of the 1913 

 lot might be interpreted to be a size change or evolutionary change 

 occurring in a period of 7 years, but I believe it is more likely the 

 result of an error due to the small number of shells or to the collecting 

 of the shells in a locality slightly different from, or lower than, that 

 where later collections were made. 



As in the case of A. mustelina Mighels (Welch, 1938, p. 142), I do 

 not believe any evolutionary change has brought about a difference in 

 the size of shells of A. apexfulva collected 20 years ago and those 

 collected in the same locality today. This differs from Crampton's 

 (1916, 1932) findings in his study of Partula of the Society Islands. 



E. Dextrality and Sinistrality 



No order is found in the occurrence of dextral and sinistral forms 

 either horizontally or vertically. Ridge complexes 15-20 are domi- 



