110 ORTMANN— AFFINITIES OF CAMBARUS. 



[April i 3) 



{rarely shorter} and more or less strongly curved backward, both in 

 the same direction. Always only the third pereiopods with hooks 

 {barring freaks'). 



The shape of the sexual organs is quite uniform in this section, 

 and they do not vary much in the different species, with one excep- 

 tion : C. difficilis. Here they are remarkably short and stout, 

 reaching only to the third pereiopods. But we cannot separate 

 this species on this account from the section, since in other charac- 

 ters it is closely allied to C. palmeri. 



This section closely approaches the propinquus type, especially 

 that represented by C. rusticus, in fact, the curvature of the tips of 

 the sexual organs is the only important differential character. Be- 

 sides, however, there is in no case a shoulder developed here, 

 which is so frequently seen in the propinquus-section. 



In other characters this section is more variable than the propin- 

 quus-section, and this is most evident in the width and length of 

 the areola. The chelae are built according to the type of the 

 propinquus-section, but a remarkable character is the presence of a 

 dense tuft of hairs {beard) at the base of the immovable finger. 

 This beard is absent in C. compressus only. In two species, C. 

 alabamensis and compressus, the chelae are very broad, and excep- 

 tionally smooth. 



The annulus of the female is depressed in the middle, with 

 raised margins, similar to that of some species of the propinquus- 

 section (virilis, longidigitus) . In other cases it is elevated posteri- 

 orly, and the anterior part is depressed ; it is never elevated ante- 

 riorly, as is generally the case in the propinquus-section. (In some 

 species, alabamensis and mississippiensis, the description of the 

 annulus is inadequate). 



The eleven species of this section are easily arranged into three 

 groups according to the areola. 

 i. Group: {alabamensis). 



Areola wide a fid short. 



2. Group : (virilis'). 



Areola narrow, of medium length. 



3. Group.- {palmeri). 



Areola obliterated in the middle, of medium length. 



4. Section : C. lancifer. 



Sexual organs very peculiar ; short, and with slightly curved tips, 

 the outer tip remarkably compressed. 



