Excerpt from Pimelodella and TyphlobagrusThe 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 Pimelodclla becomes a delicate and ditfi cult task. The following definitions, especially as far as they concern species of the Amazon Basin, are therefore more or less tentative.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.