1919*] 
New Zealand Institute Science Congress. 
265 
The characters used for discriminating species and subspecies are chiefly 
form, ornament, and colour. Other characters which may be useful are 
the nature of the muscular scar and of the radula. 
Form .—There are three main elements in form : (1) The outline, whether 
broadly or narrowly oval, elliptical, or circular; (2) the position of the apex, 
whether near or distant from the front margin ; (3) the height of the 
shell, whether low (depressed) or high (conical). 
The form must be considered from the point of view of its development. 
In very young shells the apex is quite anterior, and during growth it 
gradually recedes from the front margin. In shells of the same size it 
has receded in some farther than in others. These may therefore be 
considered as more advanced in form than the latter, or we may say that 
the latter are arrested juveniles of the former. 
In outline the shells of this group are always narrower towards the 
front— i.e., the shape is ovate; but the shells broaden behind with age. 
We may therefore regard narrow, long shells as less advanced than broad 
shells of the same length. In general the shells do not accommodate 
themselves to accidental depressions in the rocks, but occasionally they 
do, and then the shape becomes irregular in outline. 
The high conical shells go through a depressed stage with an anterior 
apex. They are therefore more advanced in form than the depressed 
adult shells, and deserve specific recognition on this account. The species 
jperana and flava belong here. Perhaps an intermediate species should be 
recognized. The type of radians is a depressed form. 
Ornament .—Three main types may be recognized, which may be termed 
smooth, striate, and ribbed or folded. These terms are, however, only 
relative, even the apparently smooth shells being microscopically striate. 
In general the folded shells show a development from smooth through 
striate to folded, but occasionally the striate stage appears to be suppressed. 
In the depressed C. radians adult shells may be smooth, striate, or folded. 
In many localities the conical C. perana is always folded when adult, but 
in others it is only striate. I have never observed it smooth. 
Colour .—There are two main types of colour-pattern, with many inter¬ 
mediates. The one consists of simple radial brown lines, broken or con¬ 
tinuous, following the main ribs. The other consists of alternately brown 
and colourless broad or narrow bands crossing the shell at an angle with the 
ribs, and generally divaricating. This latter is found on the type of the 
subspecies earli, and may be termed the 44 earli ” pattern. A third type 
according to colour includes shells without any colour-pattern. These 
variations in colour and pattern have been extensively used in the dis¬ 
crimination of the subspecies. 
As a matter of fact, a shell may alter its pattern during growth. It 
may change from radial to 44 earli ” pattern or vice versa, or it may lose 
colour-pattern altogether for a period and then resume it. Obviously, 
therefore, the pattern can be used for classificatory purposes only with 
great caution. Colour-pattern is not a character in which there is 
continuous development in a definite direction. Moreover, the patterns 
repeat themselves in a similar manner in both depressed and conical forms. 
The 44 earli ” pattern is not so common on conical shells, but it is occasion¬ 
ally well exhibited, while shells without colour-markings are commoner in 
conical than in depressed forms. 
Before discussing the significance of the colour and pattern and its 
relation to environment it is of interest to note the probable mechanism 
