122 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
(2) The color characters are naturally more complex. First of allis the division 
into plain and banded types; the bands are revolving stripes, always of a darker 
color entirely different from the strigations that run longitudinally, as the systema- 
tists describe them (plate 25, figs. 38 and 39). Actually, on the basis of internal 
structure, the bands should be called longitudinal and the strigations transverse, 
but the terminology of the taxonomists who have dealt primarily with the shell will 
be employed nevertheless. 
Of the plain shells, four classes are distinguishable on the basis of the general 
ground-color, which may be yellowish (Class I, plate 25, figs. 1 to 7), fulvous yellow 
(Class II, plate 25, figs. 8 to 18), reddish brown (Class III, plate 25, figs. 19 to 28), or 
brownish, with or without some addition of red (Class IV, plate 25, figs. 29 to 37). 
These classes merge into one another through intermediates, but the majority of the 
shells group themselves about the four typical colors as given. Strigations of the 
transverse order may or may not be present. They occur more abundantly on the 
shells with darker ground-colors. 
The apex of the spire may be of the same hue as the rest of the shell, or it may 
be deeply stained to a purplish red. The deeply colored apex may occur on a light 
shell or on one with darker ground-colors. 
The lip and its adjacent lining may be pure white, as in the great majority of 
cases, or it may be uniformly suffused with light purple, or purplish brown. 
In dimensions the shells vary so as to present a curve of error in all of the seven 
characters defined in the cases of hyalina, clara, and nodosa. It is not possible to 
make a qualitative or alternative classification on the basis of these characters. 
Finally, the pillar tooth may be absent, present as a diminutive process, present 
and well-marked, large or very large. 
In summary, then, the more or less independent characters of the Fautaua 
shells may be tabulated as follows: 
Coil: Sinistral : Dextral. 
Color: 
Basispaqs cere eet nc I. Yellowish: II. Yellow-fulvous: III. Reddish: IV. Brown. 
Bandsey ener cere Present : absent (=‘“‘plain’’). 
Sthipations = 5-— es Present : Absent. 
Apex: .02 Re tatan aes Unmodified : Tinged. 
i pes cr ures cetieee White : Tinged. 
Dimensions: 
Wiholelshellenee nece Variable continuously. 
Apertureletss «cme nieias Variable continuously. 
Proportionss14- ci 2)4-1: Variable continuously. 
ADyatoxd WOR Mary ot ata col fe Absent : Trace : Average: Large: Very large. 
A given individual possesses a group or combination of characters, each of 
which is one of the two or more possible qualities under a given head. Thus one 
shell is dextral, unbanded, reddish (Class III), strigated, with tinted apex, white lip, 
and above the average in the dimensions of the whole shell, below the average in 
aperture dimensions, and devoid of a tooth; another presents some of the above, 
together with alternative or at any rate distinctively different qualities in other 
respects. Hence no single shell and no small number of shells could be justly 
regarded as a “type” or as “typical,” for we must take into account all of the varied 
