112 MEMOIRS OF THE CARNEGIE MUSEUM. 



The family Gymnotidce, as discussed in this monograph, includes all of the 

 species of the two families, the Gymnotidce and the Electrophoridce as restricted by 

 Gill. The electric eel, Electrophorus eledricus Linnaeus, has been included in this 

 family for two reasons. Its affinities with Gymnotus carapo Linnaeus are very 

 close, and it is more closely related to the other Gymnotids than to any other 

 group of fishes. The relation of E. eledricus to G. carapo is shown by the following 

 comparison. 



I. Characters Common to Both Genera. 



Depressed head; body subcylindrical and elongate; teeth large, in one or two 

 rows in each jaw, conical, in sockets; lower jaw shghtly projecting; eyes small; 

 no frontal fontanel; parietal fontanel small and almost covered by the overhanging 

 occipitals; posterior air-bladder long and conic; origin of anal fin just below tips 

 of pectorals; anus below gill-opening. 



IL Characters Restricted to Electrophorus. 



Anal turned up so as to form a false caudal; scales wanting; electric organs 

 well developed. 



III. Characters Restricted to Gymnotus. 



A small caudal appendage projecting beyond the anal fin; no electric organs, 

 or at least only indications of Hunter's organs; scales present. 



It will be seen that the presence of electric organs is the point of largest differ- 

 ence between Electrophorus and Gymnotus and as pseudo-electric organs are known 

 for other species of the Gymnotidce, it does not seem that Electrophorus should 

 stand in a separate family. Plate XVI shows two views of the skull of G. carapo. 

 That of Electrophorus is the same in almost every detail, except that it is more 

 depressed. 



Three subfamilies are recognized. The Gymnotince just discussed, the Sterno- 

 pygince, and the Sternarchince. The last two named differ from the first especially 

 in two particulars: they are compressed and have both frontal and parietal fon- 

 tanels. The Sternopygince differ from the Sternarchince in the absence of a caudal 

 fin. These two subfamilies parallel each other quite closely in their variations. 

 Plate XV shows an outline of the head of a typical species of each genus of the 

 family. The parallelism of the Sternopygince and Sternarchince is particularly 

 evident in the development of long-snouted forms, short-snouted forms, and 

 toothless forms. Plates XVII and XVIII show the modification of the skull in the 

 long-snouted Rhamphichthys rostratus as compared with the short-snouted Eigen- 

 mannia virescens, both fishes being of the subfamily Sternopygince. These plates 

 may be compared with Plate XV as regards the presence or absence of the frontal 

 fontanel. 



Boulenger (Archiv fiir Naturgeschichte, Jahrgang 1904, Bd. I, Heft 2) con- 

 siders the Gymnotidce as an offshoot from the Characidce. The Gymnotidce seem to 



