18 A REVISION OF THE ASTACIDA. 
The section of the carapace behind the cervical groove is more than half 
as long as the distance from the cervical groove to the tip of the rostrum, as 
in C. Blandingi’, etc., or much less than half this distance, as in C. versutus, ete. 
In ©. spiculifer, C. versutus, and C. pubescens, the areola is broad, as in the genus 
Astacus. In the majority of the species of Cambarus the areola is narrow, or 
even obliterated by the close approximation of the branchio-cardiac lines in 
the median line of the back, as in C. Diogenes, C. Clarki, ete. The narrow- 
ing of the areola involves an increase in height of the branchial chambers, 
for the so-called branchio-cardiae lines which form the lateral boundaries of 
the areola denote the upper limit of the branchial chamber where the lining 
‘membrane of the carapace is continued into the lateral wall of the thorax. 
This increase in the height of the branchial chamber which generally obtains 
in the genus Cambarus may perhaps be explained as a means to allow an 
increase in the length of the branchiz in compensation for the diminution 
in number. The broad areola which accompanies the more generalized gill 
formula of Astacus may be considered the more primitive form. In accord- 
ance with this view, it appears that in species of Cambarus with very narrow 
or linear areola, as C. Clarkii, the very young stages of growth display an 
appreciably wider areola. 
The antennal scale in the species of Cambarus belonging to the first 
group is commonly broadest toward the base or at the middle. 
' The most aberrant species of the group are C. pemcillatus, C. Allen’, and 
C. pellucidus. In C. penicillatus and C. Alleni the rostrum is devoid of lateral 
teeth, the spine that terminates the inner part of the first abdominal appen- 
dages of the male is long and erect, the terminal teeth minute. In C. peni- 
cillutus the antennal lamina is short, and broad toward the tip. The blind 
C. pellucidus, from the caves of Kentucky and Indiana, is the most peculiar 
species of the group. The sides of the rostrum are sub-parallel from the 
base to the lateral spines, the acumen long; the antennal scales are broadest 
at the distal end; the portion of the carapace which lies in front of the cer- 
vical groove is very short compared with the hinder section. The first pair 
of abdominal appendages of the male are hardly specialized to a greater de- 
gree than in the genus Astacus, the tips of the organs being simply produced 
into two small processes, the one representing the spine that terminates the 
inner part of the appendage in the more normal species of the group, the 
other the teeth of the outer part. In the first form of the male the latter 
process 1s corneous. The appendage, as a whole, is more closely rolled than 
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