Osteology and Relationships of South AmericanCharacid Fishes of Subfamilies Lebiasininae and Erythrininae with Special Reference to SubtribeNannostomina

Proceedings of the United States National Museum SMITHSONIAN INSTITUTION . WASHINGTON, D.C. Volume 116 1964 Number 3499 OSTEOLOGY AND RELATIONSHIPS OF SOUTH AMERICAN CHARACID FISHES OF SUBFAMILIES LEBIASININAE AND ERYTHRININAE WITH SPECIAL REFERENCE TO SUBTRIBE NANNOSTOMINA ^ By Stanley H. Weitzman Introduction The present work is the result of an attempt to determine the relationships of two characid genera, Nannostomus and PoecUobrycon, to other members of the cypriniform family Characidae. The two genera include about eight known species of small characids found in forest brooks of South America. These species are here assigned to the subtribe Nannostomina. Although the first known species of this group was described in 1872, adequate investigation of morpho-logical evidence for their relationships has never been undertaken. Previous investigations have been superficial in scope and often inaccurate in fact primarily because of the small size of these fishes. The total cranial length is usually 5-10 mm, and the largest recorded specimen is 44.5 mm. in standard length. In some cases, despite the lack of adequate morphological data, certain ichthyologists have ' This paper is the second of three parts based on a dissertation submitted to the Department of Biological Sciences, Stanford University, California, in partial fulfillment for the degree of Doctor of Philosophy. See Weitzman (1962) for the first part. 127