PROCEEDINGS OF THE NATIONAL MUSEUM. 631 



Cambarus nais Fax. 



Cambarus nais Faxon, Bull. Washburn Coll. Lab. Nat. Hist., Topeka, Kansas, 

 Vol. i, 1885, pp. 140, 141. 



Male, form I. — Bostrum long, concave above, lateral margins con- 

 verging from the base to the lateral spines, which are small but dis- 

 tinct ; acumen of moderate length, acute. Post-orbital ridges provided 

 with a minute anterior spine. Carapace smooth and lightly punctate 

 above, granulate on the sides; lateral spine small, acute; cervical 

 groove sinuate, ending anteriorly in a small branchiostegian spine; 

 suborbital angle not prominent; areola very narrow, punctate, tlie 

 margins parallel from the anterior to the posterior triangular fields; 

 the length of the areola is equal to one half the distance from the tip 

 of the rostrum to the cervical groove. Abdomen as long as the ceph- 

 alothorax. Proximal segment of the telson bispinose on each side, 

 distal segment shorter than the proximal. Antennae longer than the 

 body; laminae a little longer than the rostrum, broad, broadest at the 

 middle, subtruncate at the end, with an external apical spine. Third 

 maxillipeds densely setose within and below. Anterior process of the 

 epistoma with very convex sides. Chela broad, flattened above, punc- 

 tate, external border marginate; inner margin of the hand short, with 

 a double row of dentiform tubercles ; fingers long, movable one tuber- 

 culate on the external border, toothed on the internal border ; external 

 finger flat above, internal margin toothed, and bearded at the base. 

 Corpus armed with a row of small tubercles on the upper side, with a 

 strong and acute internal median spine and a small one at the base; 

 on the lower side the carpus is provided with a prominent median spine 

 and an external one at the point of articulation with the chela ; in some 

 specimens there is a small spine on the lower face of the carpus, between 

 the median spine and the large one on the internal margin. Third pair 

 of legs armed with a hooked tubercle on the inner margin of the third 

 segment. First pair of abdominal appendages of moderate length, 

 twisted, deeply bifid, very broad in the middle; rami slender, styliform, 

 strongly recurved, the inner one a little shorter and more curved than 

 the outer one, the outer one corneous. Length, 57 mm ; cephalothorax, 

 27 mm ; from tip of rostrum to cervical groove, 18 mm ; from cervical 

 groove to posterior border of carapace, 9 mm ; abdomen, 30 mm ; chela, 

 24 mm ; width of chela, 10 mm . 



The second form of the male differs from the first form in having 

 smaller chelae, the tubercles on the third pair of legs less developed, 

 the first abdominal appendages less deeply cleft, the rami stouter, 

 blunter, and not corneous. 



In the female the chela is similar to that of the second form of the 

 male, the sternum between the fourth pair of legs is smooth, the annu- 

 lus ventralis triangular with a median longitudinal fissure. 



