ANNOTATED LIST OF THE SPECIES 83 
Type: Pastinaca humboldtii Roulin 
The fresh waters of South America 
Mouth papillose, teeth in more than twenty-five rows, tail spiny, length of 
spines irregular, one or more long. 
1. PorAMOTRYGON HysTRIx (Miiller and Troschel) 
Pastinaca humboldtii Roulin, 1829, Amer. Sci. Nat., X VI, 104, pl. iu; 
Duméril, 1865, Hist. Nat. Poiss., I, 625. 
Trygon hystrix Miiller and Henle, 1841, Syst. Beschr. Plagiostomen, 167; 
Valenciennes, in D’Orbigny, 1847, Voy. Amer. Merid., V, 11, 11, pl. xv, La Plata to the 
Amazon; 
Castelnau, 1855, Anim. Amér. Sud, Poiss., 103; 
Giinther, 1870, Cat. Fish. Brit. Mus., VIII, 482. 
Potamotrygon humboldtii Garman, 1877, Proc. Boston Soc. Nat. Hist., 210; 
Zigenmann, 1910, Rept. Princeton Univ. Exped. Patagonia, III, 378. 
Potamotrygon hystrix Eigenmann and Kennedy, 1903, Proc. Acad. Nat. Sci. Phila., 498; 
Fowler, 1939 (1940), Proce. Acad. Nat. Sci. Phila., XCI, 221, Contamana. 
Trygon miilleri Castelnau, 1855, Anim. Amér. Sud, Poiss., 102, pl. xlvii, fig. 2. 
Guianas to La Plata and Rio de Janeiro 
16137, 2, 108 and 232 mm., Rio Ucayali, near Orellana, Allen, August, 1920. 
16138, 2, 123 and 240 mm., creek, Yurimaguas, Allen, November, 1920. 
16139, 3, about 180 mm., Yarinacocha, Allen, August, 1920. 
The three specimens numbered 16139 were given birth when the mother was 
taken by seine. Yolk sacs were still attached, but nearly used up. Two males 
and a female. 
The only selachian species collected, it represents the sole species of its class 
(which is almost completely marine) at this remote distance from the sea, and one 
of a considerable number of fishes owing their origin to the salt water era in the 
history of the Amazon. 
Order NEMATOGNATHI, the Cattfishes 
Fishes without scales, naked or with bony plates; first four vertebrae united 
to form Weberian apparatus; subopercle lacking; maxillary reduced to mere basis 
for barbel; teeth in villiform bands; dorsal fin usually present and above or before 
ventrals; adipose fin usually present, variable; air bladder present, large, united to 
Weberian ossicles; first dorsal and pectoral fins usually extremely developed. 
These fishes find their greatest numbers of species and individuals in the freshwaters 
of South America; there as elsewhere they are noteworthy for extreme tenacity 
of life. 
Family II: Aspredinidae 
Nematognath fishes having vestigial opercle; body expanded forward to form 
distinct trunk and tail regions, much depressed; neural spines of the coalesced 
vertebrae forming a ridge from the occipital region to the dorsal fin; caudal verte- 
