EIGENMANN: PIMELODELLA AND TYPHLOBAGRUS 231 
armature of the pectoral spine, the shape of the caudal lobes, and a number of 
other minor characters. 
The length of the barbels in the same species differs with age. In the young 
the barbels are relatively short. They grow disproportionately longer with the 
growth of the fish and then lag behind again in their increase in length. The 
length of the barbels of the same species not only differs with age, but sometimes 
also with locality. The pectoral spines also vary somewhat with growth. With 
age the thorns increase in number by the addition of new ones toward the tip 
and come to occupy a larger portion of the length of the spine. The spine in- 
creases in length by the addition of new sections at the end which are marked off 
by notches or hooks on the outer margin of the spine. As the color and the size 
of the eye also vary with age and with locality, and, as all of these characters vary 
independently, the defining of species of Pimelodella becomes a delicate and diffi- 
cult task. The following definitions, especially as far as they concern species of 
the Amazon Basin, are therefore more or less tentative. 
Most of the species are small. The largest species of the Atlantic slope is 
P. cristata with a recorded length of 340 mm. The largest species from the Pacific 
slope is P. eutenia of which I have examined specimens 188 mm. long. 
The following notes may help to identify the species. Species in which the 
barbel extends to caudal are: gracilis, notomelas, serrata, mucosa, boliviana. 
Species in which the pectoral spine is smooth or very feebly serrate are: roc- 
ce, filamentosa, eigenmanni, meeki, vittata, buckleyi, boliviana, eutenia, notomelas, 
mete, itapicuruensis, hartti. 
Species in which the pectoral thorns are moderate are: cristata, gracilis, avan- 
handave, puruensis, laticeps, australis, vittata, mucosa. 
Species in which the pectoral thorns are very strong are: lateristriga, serrata, 
hasemani, mucosa, chagresi, macturki, megalops, modesta, grisea, pectinifera, cyano- 
stigma, transitoria. 
Key to THE Cis-ANDEAN SPECIES OF PIMELODELLA.? 
a. Head without conspicuous mucous pores. 
b. Adipose fin usually less than three in the length, extending beyond the tip of the anal fin. 
c. Pectoral spine with strong teeth both in front and behind; maxillary barbel extending 
beyond base of anal or caudal.......:..............-....-.----l. serrata Higenmann. 
ce. Pectoral spine with moderate thorns on the posterior margin, but slightly serrate or rough- 
ened along the anterior margin. 
d. Lower caudal lobe much broader than the upper, upper lobe not produced, the 
lower frequently the longer; lateral band if present narrow, linear; 13-14 teeth 
2 The species found east of the eastern Andes of Colombia and the Atlantic slope of Ecuador and 
southward. See in this connection P. chagresi, p. 253. 
