100 ORTMANN — AFFINITIES OF CAMBARUS. [April i 3 , 



tively of C. gracilis and of C. advena (Hyeme vitam degit subter- 

 ranean!. Aestate in fossis invenitur. Leconte). 



The large number of species known in the third section makes a 

 further division desirable, which is easily made according to the 

 following characters : 

 i. Group : {spicu lifer) . 



Outer part of sexual organs with two or three recurved teeth, with- 

 out prominent angle {shoulder) on anterior margin. Rostrum with 

 marginal teeth, acumen rather long. Areola wide, rarely narrow, 

 distinctly shorter than half of the anterior section of the carapace. 

 2. Group: {blandingi). 



Outer part of sexual organs with three {rarely two) recurved 

 teeth, inner part with terminal spine directed obliquely outward. No 

 shoulder on anterior margin. Rostrum with marginal teeth, acumem 

 rather short. Areola narrow, generally distinctly lunger than half 

 of the anterior section of the carapace. 

 j. Group: {clarki). 



Outer part of sexual organs with two compressed tubercles, inner 

 part straight, directed forwards. Anterior margin with a distinct 

 shoulder. Rostrum with marginal teeth, acumen rather short. 

 Areola very narrow, often obliterated in the middle, about half as 

 long as anterior section of carapace. 

 4. Group : {alleni) . 



Outer part of sexual organs with one or tiuo teeth, often peculiarly 

 formed {compressed and plate-like), inner part straight or oblique. 

 No shoulder on anterior margin. Rostrum without marginal teeth 

 {at least in the adult stage). Areola moderately wide, about half as 

 long as anterior section of carapace. 



There is no doubt, that the spicu lifer-group is the most primitive 

 of these, and that the others represent special modifications, each 

 developed in a different direction. 



The following key for the identification of the species of the sub- 

 genus Cambarus is submitted ; it is claimed that this key represents 

 — as far as is possible in a " key " — the natural affinities. If adult 

 males of the first form are at hand, it should be possible, in every 

 case, to correctly identify the species. 

 1. Section of C. digue ti (see p. 98). 



flj Sexual organs of male with only one terminal tooth on outer part, inner part 

 with two tips ; anterior margin with an angular projection (shoulder ) near 

 the tip {digueti-group). 



