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. eutmnia 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, holiviana. 



Species in which the pectoral spine is smooth or very feebly serrate are: roc- 

 coB, filamentosa, eigenmanni, meeki, vittata, buckleyi, holiviana, eutcenia, notomelas, 

 metce, itapicuruensis, hartti. 



Species in which the pectoral thorns are moderate are: cristata, gracilis, avan- 

 handavce, 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. 



6. 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 1. serrata Eigenmann. 



cc. 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 



^ 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. 



