478 PROCEEDINGS OF THE NATIONAL MUSEUM vol.88 



spines slight or indicated by protuberances at base 

 of fii-st antennae as are the postantennal spines ; 

 supporting ribs of suction cups tapering, composed 



of 9 or 10 segments ; fresh water, Brazil salminei (p. 502) 



6^ Smaller respiratory area mesial to larger or in an antero- 

 mesial notch of latter. 

 c\ Spine present at the base of first antennae. 

 (f. Three spines in a row on each side of midline of body, 

 including those at base of first antennae. 

 e^. Smaller respiratory area located anteromesially in a 

 notch of the larger one, both posterior to the second 

 maxillae ; supporting ribs of suction cups composed 

 of 2 or 3 segments ; distal lobe on basal plate of second 

 maxillae blunter and wider than others; basal seg- 

 ment of first antennae usually prolonged into a knob 

 directed toward the midline of body ; fresh water. 



anaericanus (p. 504) 

 e". Smaller respiratory area in a notch proximal to and 

 some distance behind anterior end of larger ; support- 

 ing ribs of suction cups composed of more than 2 

 segments. 

 f. Second maxillae with slender teeth of basal plate 

 widely spaced; first segment of supporting ribs of 

 suction cups elongate and narrow followed by 2 or 

 3 oblong ones ; knob present on anterior surface of 

 first antennae ; carapace reaching abdomen ; ab- 

 domen subtriangular ; fresh water versicolor (p. 505) 



f. Teeth of basal plate on second maxillae close together 

 and long ; supporting ribs of suction cups composed 

 of a rectangular basal and 2 distal segments in male 

 and 4 to 7 in female ; anterior hook present on first 

 antennae ; carapace extending to third appendages ; 

 abdomen somewhat rectangular ; fresh water. 



maculosus (p. 507) 

 d^. Postantennal spines 2, suction cups with about 5 slender 

 segments in ribs extending two-thirds of width of rim 

 of disk ; lateral hook of first antennae curved in an arc, 

 tip of first antennae biramous ; postmaxillary spines 

 very small ; broad posterior lamellae on basis and coxa 

 of fourth thoracic appendages ; animal characteristically 

 broad and leaflike in appearance ; fresh water. 



mississippiensis (p. 509) 

 c^. No spine at base of first antennae. 



d\ Basal plate of second maxillae lobed or with slender 



blunt teeth ; no spine on ventral surface of first antennae 



or at base of first or second antennae. 



e\ Basal plate of second maxillae with 2 to 4 lobes, usually 



3, postmaxillary spines absent; anterior knob present 



on first antennae; ribs of suction cups with 7 to 9 



short rods, fresh water castostomi (p. 511) 



el Three slender blunt teeth on basal plate of second maxil- 

 lae ; only a slight indication of a knob on the anterior 

 surface of the first antennae, tip of flagellum biramous ; 



