ASTACID^E. 29 



ogous to the form in Astacus, but produced in a different and exagger- 

 ated manner. The hinder part of the sternum is separated and curved, 

 not backward, as in Astacus, but forward and entirely rolled. 



I may remark that, according to my anatomical investigations into 

 some species, the internal sexual parts in males and females of Cam- 

 bams differ from those in Astacus. The three lobes of the testicles and 

 the ovarium are larger, rounded, and closely approximated in Astacus, 

 the vasa deferentia longer than the body. In Cambarus the three lobes 

 are small, elongated, and separated ; the vasa deferentia shorter than 

 the body. 



It would be very interesting to prove that the young of the genus 

 Cambarus are hatched from the eggs in a similar but more advanced 

 stage of development than the young of the genus Astacus, described by 

 Professor Rathke. But the materials in my hands are not sufficient for 

 this purpose, the smallest seen by me being 0.3 inches long, and be- 

 longing to C. Clarkii. The rostrum is incurved, but always tridentate ; 

 the interior antennas have the nagellum short, and the exterior branch 

 visibly thicker than the interior. The three anterior pairs of legs have 

 nearly the same shape, the first pair is a little longer. The appendage to 

 the legs of the young lobster, described by Thompson, Rathke, and others, 

 does not exist at all. The abdominal legs do exist. The hooks on the 

 third and the fourth pair of legs of the males are not developed. It is 

 easy, as I have before intimated, to discriminate between the two sexes. 

 The eyes are visibly more developed than in the more advanced ani- 

 mals. 



With reference to the further division of the genus Cambarus, it was 

 especially important to decide whether all North American Cambari be- 

 longed to the same genus or to different genera. I am now convinced 

 that all the species I have seen form only one genus, containing several 

 more or less well-defined groups. In this manner the genera Cambarus 

 and Astacus seem very natural and of equal value. But I have no 

 doubt that some time the genus Astacus will be divided into three gen- 

 era (for the European, North American, and Asiatic species), and Cam- 

 barus into three or it may be into six genera as Prof. Agassiz thinks. 



The division of Cambarus into groups is not difficult, except in a cer- 

 tain view : first, as the most striking characters are to be found only in 

 one sex, in the males; and secondly, as some species seem to form a sort 

 of medium uniting the different groups. The first objection is only of 

 value to the naturalist who works with few materials, perhaps mostly 

 females, and is therefore not able to determine the groups to which his 

 specimens belong. But here the fault lies only in the scantiness of his 

 materials, and not in the principle of classification. The second objec- 

 tion would be more important if it were quite certain that there are 

 intermediate species. Perhaps these species only seem to be inter- 



