18 A HE VISION OF THE ASTACID.E. 



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. Bhiiilingii, etc., or much less than half this distance, as in C. vcrsutus, etc. 

 In C. xpiculifer, C. vcrsutus, and C. pulescens, the areola is broad, as in the genus 

 Astacns. 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. Ctarkii, etc. The narrow- 

 ing of the areola involves an increase in height of the branchial chambers, 

 for the so-called branchio-cardiac 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 branching 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. Clarldi, the very young stages of growth display an 

 appreciably wider areola. 



The antenna! 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. pcnicillatus, C. Alleni, and 

 C. pcllitcidus. In C. penicilMus 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. pcui- 

 cHlultis the antennal lamina is short, and broad toward the tip. The blind 

 C. pdhiciilns, 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 is corneous. The appendage, as a whole, is more closely rolled than 



