FRESH-WATER CRABS OF AMERICA— RATHBUN. 513 



any other character. With regard to the general ai)pearance of tlie 

 carapace, reflexifrons, agassizii, and convexa are tlie most convex; 

 per II nana, f/armani, lamellifrons, and hoconrti are most llattcned and 

 are coarsely grannhite. In the remainder of the species the carapace 

 is moderately convex, often flattened in the middl<», and i)08terior por- 

 tions and gradually doHexed near the anterior and lateral margins. 

 In the following species the exognath is reduced to a short stump: 

 a(finisj agassizii, bouvieri, chilensis, conradi, dentata, denticulata, fossor, 

 ganuani, and nohilii. The following have a tubercle on the outside 

 of the manus at the base of the lingers: conradi. gannani^ magna, 

 tuberculata, tmnimanuH. 



In no two species are the abdominal appendages of the first segment 

 in the male exactly alike, but some species have similar appendages. 

 The diflforent forms may thus be briefly described and the species 

 grouped accordingly: 



1. Extremity broad, with at least one tooth or lobe on each side: 

 afnericana, belliana, dilatata, jouyi, laniellifrons, pittieri, sulci/rons^ 

 terrcHtris. 



2. Two lobes on outer side, vertically compressed, inner extremity 

 curving outwardly over these lobes: colombiana, convexa, inontana, 

 tristani, tumimanus, xantusi. 



3. One outer lobe, extremity curving outwardly over it: ecuadorensis. 



4. Comi)ressed laterally; above at extremity a large subquadrate 

 lobe which is toothed or spinous: bocourti, maxilUpes. 



5. Extremity thick, slightly compressed laterally, with outward- 

 pointing teeth : magna, richmondi. 



G. Compressetl laterally; extremity subtriangular: agrestis, denticu- 

 lata, foHsor, garmani. 



7. Upper lamina jnoduced at extremity in a slender prominence, 

 curving over broad, lower lamina: dentata, rejiexij'rons. 



<S. Outer margin with a long narrow lobe; terminus truncate, with 

 a short tooth at outer and inner angles: (vquatorialis, bouvieri, conradi, 

 Undigiana. 



9. Complex; terminal lamina oval, transverse; subtermiual lamina 

 oval, longitudinal: verticalix. 



10. Narrow; extremity small; on outer side, a dentate backward- 

 pointing lobe: tubcrculata. 



11. A deep rounded sinus on outer side near the extremity: macropa, 

 peruviana. 



12. Terminal lialf much narrower than the basal half; extremity with 

 a transverse rim of ba(;kward-i)ointing spines: bisuturalis. 



V6. Api)endages not known to me: affinia, agassizii, chilensis, exilipeii, 

 gracilipes, henrici, uobilii, plana.^ 



'The speciineu of nohilii in the U. S. National Musenm is ii fenialo; the typ«i male 

 of chiUuHiii in the I'tiris Mueouni is dried and so preserved that the rmioval of th(^ 

 iibdomim is not juacticable; of the remaining speeies, only femah's have been col- 

 lected. 



Proc. N. M. vol. xxi ;3.'i 



