348 BULLETIN 10 0, UNITED STATES NATIONAL MUSEUM 



Body, head, electric organs, and pectorals joined as subcircular disk. 

 Tail short, with fold each side. Eyes small, protruding. Mouth 

 small, protractile, surrounded by fold. Teeth small, in narrow bands. 

 Front nasal valves confluent in quadrangular flap, free behind, cover- 

 ing mouth. Gill openings narrow. Spiracles larger than eyes, close 

 behind orbits, with smooth raised edges. Skin smooth, soft, naked. 

 One dorsal. Caudal moderate, supracaudal longer. Ventrals broad, 

 distinct, inserted below pectorals. 



Concerning Bengalichthys, Annandale has the following interesting 

 remarks: "In several respects the adaptation is of a nature closely 

 similar to that which has brought about the evolution of Benthohatis 

 from Narcine, although the environment in which this evolution has 

 taken place is not the same in the two cases. Benthohatis^ as I have 

 already pointed out, is a deep-sea form — it occurs at depths from 

 about 400 to about 700 fathoms — and, like many deep-sea forms, has 

 degenerate eyes. The disk, moreover, is thick and muscular and 

 bears on the dorsal surface numerous little glandular pits; the pec- 

 toral fins are not clearly marked off from the body. In all these points 

 the species of Bengalichthys to be described immediately resembles 

 Benthohatis^ although it is not a deep-sea form, having been taken in 

 only 15 fathoms. In two striking characters, however, it differs from 

 Benthohatis^ viz, in coloration and in the number of the dorsal fins. 

 The former difference is probably owing to its environment, the lat- 

 ter to its ancestry ; in other words, the former is an adaptive character, 

 the latter a morphological one. A character common among deep-sea 

 fish of all kinds is a dark and uniform coloration of both the dorsal 

 and the ventral surface, while among the rays of shallow water it is 

 unusual for the ventral surface to be dark, although this is the case 

 in a few species. The only [then] known species of Benthohatis has 

 a dark ventral surface, the only known species of Bengalichthys a pale 

 ventral surface. The genera of the Torpedinidae, on the other hand, 

 fall naturally into several groups separated by the number (or ab- 

 sence) of their dorsal fins. Benthohatis belongs to one of these 

 groups, Bengalichthys to another. There can be little doubt, there- 

 fore, that the two genera have not had the same ancestry but have 

 become like each other owing to parallel, or rather convergent, lines 

 of evolution. Although Bengalichthys does not live in the dark 

 abysses of the sea, we may suppose that its mode of life is very similar 

 to that of Benthohatis. Neither can be a powerful swimmer, but 

 both, judging from the manner in which the muscles of the disk are 

 developed, must be powerful wrigglers and squirmers. It must be 

 remembered in this connection that the flabbiness of the flesh (i. e., 

 the muscles) of deep-sea fish which have been brought to the surface 



