52 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



Family RAJIDAE: Skates 



Body and head much depressed, united with pectorals, together 

 forming a rhomboid disk; tail rather stout, depressed, with lateral 

 folds, bearing two small dorsal fins; eyes and spiracles superior; 

 mouth small, inferior; teeth small, numerous, in pavement; skin 

 usually more or less rough, with small spines and larger tubercles. 



A single genus, as herein understood, is included in the Peruvian 

 collections studied. 



Genus PSAMMOBATIS Gunther, 1870 



Disk more or less circular, with a concavity of varying depths 

 opposite eyes and spii-acles; no rostral prolongation of the cranium, 

 the snout being soft and flexible; ventral fins definitely notched, with 

 a somewhat thickened and produced outer lobe; claspers very long, 

 slender, pointed; teeth in transverse rows, varying from more or less 

 flat to sharp and pointed, the cusps apparently larger in males than 

 females. Adult males, as far as known, have sharp spines in parallel 

 rows or in a band on the pectorals toward the outer margins of the 

 widest part of the disk. 



Each of the six species herein recognized is based on a single speci- 

 men. The specimens all seem to differ rather markedly from each 

 other and must represent species unless great variation exists that 

 cannot be determined until many more specimens are collected. 

 P. aguja differs so greatly from the others, especially in the deeply 

 notched ventral fins, large eyes, and narrow interorbital that it perhaps 

 should be considered as subgenerically distinct. It seems advisable, 

 however, to postpone such a designation until relationships are better 

 understood. 



KEY TO THE SPECIES 



a. Ventral fins deeply notched, inner lobe narrow, strongly convex; eye large, 



4.5 in snout; interorbital narrow, 3.6 in snout aguja (p. 53) 



aa. Ventral fins not deeply notched, inner lobe broad, gently convex; eye smaller, 

 4.25 to 4.9 in snout; interorbital notably broader, less than 2.5 in snout. 

 b. Disk very broad, its width 1.15 in total length; tail notably shorter than 

 rest of body; length posterior to vent 2.7 in total length; interorbital little 



concave, broad, 6.65 in length anterior to vent brevicaudatus (p. 55) 



bb. Disk narrower, its width 1 .3 to 1.4 in total length; tail longer, length posterior 



to vent, 2.2 to 2.45 in total length. 



c. Eye moderately large, about half width of interorbital, 4.25 in snout; 



preoral length of snout notably shorter than its length to eye, 4.5 in 



length anterior to axil of pectoral, and 6.85 in width of disk; color brownish 



above, with obscure pale spots caudispina, new species (p. 55) 



cc. Eye smaller, notably less than half width of interorbital, 4.7 to 4.9 in snout; 

 preoral length of snout only a little shorter than its length to eye, 4.1 

 to 4.3 in length anterior to axil of pectoral and 5.75 to 6.05 in width of 

 disk; color gray above, with more or less distinct black spots. 



