2 CALIFORNIA ACADEMY OF SCIENCES. 



specimens to make the necessary anatomical prepara- 

 tions, or to examine the osteological preparations already 

 made. 



Since 1864, the date of the publication of Dr. Gun- 

 ther's Catalogue of Fishes, no general work on the 

 Nematognathi has appeared, while the number of nomi- 

 nal South American species has been greatly increased 

 since that time. 



The Central American Siluridse, which properly be- 

 long to the South American fauna, have been omitted 

 on account of a lack of material. The same reason has 

 prevented us from giving more than lists of the genera 

 Arges, Hemiancistrus and ChaBtostomus. 



The material studied, several thousand specimens, 

 belongs to the Museum of Comparative Zoology at Cam- 

 bridge, Massachusetts, U. S. A., and was collected chiefly 

 during the Thayer Expedition, a full account of which 

 is given in Agassiz's "A Journey in Brazil."' Collec- 

 tions were made during this expedition in the coast 

 rivers from Kio de Janerio to Rio Paranahyba, and in 

 the Amazon and its tributaries from Para to Tabatinga. 

 During this expedition a valuable collection was made 

 by Senhor Vinhas in the Xirigu. A collection made by 

 Senhor Honorio in Goyaz is especially valuable as show- 

 ing the relation between the fauna of the upper courses 

 of the Tocantins with the fauna of the upper courses of 

 the San Francisco, Parahyba, Rio Doce and Rio Jequi- 

 tinhonha. The collection made by Senhor Honorio has 



*A Journey in Brazil, by Prof, and Mrs. Louis Agassiz. Boston. 

 Tichnor & Fields. 1868. Professor Agassiz was accompanied 011 this 

 expedition by the following assistants: James Burkhardt, artist; John 

 G. Anthony, conchologist; Frederick C. Hartt and Orestes St. John, ge- 

 ologists; J. A. Allen, ornithologist; Geo. Sceva, preparator; and the 

 following volunteers: Newton Dexter, William James, Edward Copeland, 

 Thomas Ward, Walter Hunnewell and S. V. K. Thayer. 



