No. 432.] STUDIES OF GASTROPODA. 933 
up all the preceding whorls. This is margined by a sharp 
elevated and thin edge. 
Varices. — Varices are the periodic rows of spines, or the 
reflexed or bent-over lips which mark recurrent stationary 
periods in growth in many gastropod shells. Several types may 
be recognized, — the spinous, e.g., Murex, the simple reflexed 
lip, best shown in Scalaria, and the periodically accentuated 
normal rib, perhaps the most abundantly represented type. 
The simplest type of the spinous varix is that in which each 
stopping place is marked by only one simple spine. Such a 
condition, found in Fulgur and a number of other genera, is 
generally not considered as falling under this category ; but it is 
clear that the multispinous varix is a modification of the uni- 
spinous one. This becomes more apparent when we note that 
in every multispinous varix one of the spines predominates over 
the others to a greater or less extent. On tracing back the spiral 
from which this spine arises, which is generally possible, even 
though the lower spines are progressively resorbed by the 
advancing inner lip of the new whorl, it appears that in every 
varix it bears the largest spine. Finally, on tracing back far 
enough, only one spine is seen on the whorl, —the primary 
spine, which throughout is recognizable by its predominant 
size. In Murex brassica Lam. of the west Mexican coast we 
have a type in which only a few additional small spines occur 
besides the primary large spine. This is but slightly advanced 
beyond the state found in Fulgur. In M. bicolor the shell con- 
tinues to grow somewhat after the chief varix is formed, the 
principal spine alone remaining unclosed, so that the lip at the 
resting stage differs little from that of Fulgur. The multispi- 
nous type of varix, with simple spines, is best illustrated in the 
beautiful Murer tenuispira Lam., the most striking in form of 
all the Murexes. Each spine arises from a spiral line, of which 
it forms the apertural prolongation. The shorter spines arise 
from the secondary spirals, and on the canal they are bent at 
about 120? forward from the primary ones, thus lying parallel 
to the primary series of the next but one varix preceding. 
Only in the neighborhood of the large spine do the tertiary and 
even later cycles of spirals terminate in small spines. 
