158 MEMOIRS OF THE CARNEGIE MUSEUM. 



Three species, Gymnotus cnrapo, Eigenmannin virescens and Sternopygus 

 macrnrus are found throughout almost the entire range of the family. Four 

 others, Hypoponms brevirostris, Hypopomus artcdi, Rlminphichthys rostr'atus and 

 Sfcrnarchus albifrons, have an almost equally wide distribution. The remaining 

 species are confined largely to the Amazon system and the Guianas. Twenty- 

 foui- of the twenty-seven species are found in some part of the Amazon system and 

 lifteen speci(»s are listed from the Guianas. The combined Amazon and Guiana 

 faunas include all of the species of the family with the single exception of Steniarchus 

 brasiliensis. This species is known only from the Rio San Francisco and its tribu- 

 taries and is restricted to the higher parts in the region of the Sierra Matta da 

 C^ordc. 



The Gyinnoiida.', are largely lowland fishes as is shown by the steady decrease in 

 the number of species as the Amazon is ascended. This of course may be due in 

 part to incomplete exploration. In places when the faunal survey has been quite 

 ('omplt>te, however, they are largely found in the lowland. Of the fifteen species 

 known from British Guiana all are found in the lowland, while but two, Gymnotus 

 carapo and Eigenmannia virescens, have been taken on the plateau. 



Locomotion and Musculature. 



I. Locomotion. 



The method of swimming, particularly the use of the long anal fin, of the 

 Gymnotidce has been discussed several times. No final conclusion has been reached, 

 however. In 1774 Alexander Garden described the method of swimming of the 

 electric eel. He worked at Charleston, S. C., with five specimens which had 

 been shipped him from Surinam. The motion of the fish, according to Garden, was 

 the result of an undulating movement of the anal fin. This has subsequently been 

 shown to be correct by Sachs. Unfortunatelj- Lac^pede misquoted Garden in 

 his "Histoire Naturelle des Poissons" published in 1800, by ascribing the undu- 

 lating motion not only to the anal fin but to the body of the eel as well. As a result 

 of this the exact use of the anal fin remained in doubt imtil the careful work of 

 Sachs (Zitteraal, 1881). He described the swimming of the electric eel in detail as 

 follows : 



"Die Zitteraale sind ausnehmend gewandte Schwimmer und zwar schwimmen 

 sie gewcihnhch nicht durch Schlangeln des Schwanzes, wie Lacepede anninunt, 

 sondern einzig und allein unter Anwendung der weichhautigen, dem Kiel eines 

 Schiffes gleichenden Afterflosse, welche durch die Brustflossen in geringemgrade 

 unterstiitzt wird. Die Bewegung der Afterflosse besteht in einer wellenformigen 

 Schliingelung; luuft die Wellen von vorn nach hinten so wird der Fisch vorwilrts 

 bewegt, Uluft sie umgekehrt, so schwimmt er riickwiirts; die Bewegung ist geradlinig 

 oder bogenformig, je nachdem der Korper des Fisches ausgestreckt oder gekriimmt 

 ist" (p. 104, 1. c.). Sachs neglected to observe the method of swimming of the 



