158 MEMOIRS OF THE CARNEGIE MUSEUM. 
Three species, Gymnotus carapo, Eigenmannia virescens and Sternopygus 
macrurus are found throughout almost the entire range of the family. Four 
others, Hypopomus brevirostris, Hypopomus artedi, Rhamphichthys rostratus and 
Sternarchus albifrons, have an almost equally wide distribution. The remaining 
species are confined largely to the Amazon system and the Guianas. Twenty- 
four of the twenty-seven species are found in some part of the Amazon system and 
fifteen species are listed from the Guianas. The combined Amazon and Guiana 
faunas include all of the species of the family with the single exception of Sternarchus 
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 
Corde. 
The Gymnotide 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 
complete, 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 Higenmannia 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 
Gymnotide 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, 8. 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. Unfortunately Lacépéde 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. Asa result 
of this the exact use of the anal fin remained in doubt until 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 gewOhnlich nicht durch Schlingeln des Schwanzes, wie Lacépéde annimmt, 
sondern einzig und allein unter Anwendung der weichhautigen, dem Kiel eines 
Schiffes gleichenden Afterflosse, welche durch die Brustflossen in geringemgrade 
unterstitzt wird. Die Bewegung der Afterflosse besteht in einer wellenférmigen 
Schlingelung; lauft die Wellen von vorn nach hinten so wird der Fisch vorwiirts 
bewegt, liuft sie umgekehrt, so schwimmt er riickwiirts; die Bewegung ist geradlinig 
oder bogenférmig, je nachdem der K6rper des Fisches ausgestreckt oder gekriimmt 
ist’? (p. 104, Ll. ¢.). Sachs neglected to observe the method of swimming of the 
