340 FISHES. 



and emit the spark. The dorsal surface of the electric organ 



is positive, the ventral surface negative. 



[The literature on the electric organ of Torpedo is very extensive. 

 Here may be mentioned Lorenzini, ' ' Osservazioni intorno alle 

 Torpedini (1678) ; Walsh, "On the Electric Property of the Tor- 

 pedo," in Philos. Trans., 1773; Hunter, "Anatomical Observa- 

 tions on the Torpedo," ibid.; Davy, "Observations on the 

 Torpedo," in Philos. Trans., 1834; Maiteueoi and Savi, "Traits 

 des Phenom^nes Electro-Physiologiques," 18i4.] 



Of the genus Torpedo six species are known, distributed 

 over the Atlantic and Indian Oceans ; three of them are rather 

 common iu the Mediterranean, and one {T. hebetans) reaches 

 the south coast of England. They attain to a width of from 

 two to three feet, and specimens of that size are able to dis- 

 able by a single discharge a full-grown man, and, therefore, 

 may prove dangerous to bathing persons. Other genera, 

 differing from Torpedo in the position and structure of some 

 of the fins, are found in other tropical and sub-tropical seas, 

 viz. JVarcine, Hypnos, Discopyge (Peru), Astrape, and Temera. 

 All, like electric fishes generally, have a naked body. 



A large fish, of the general appearance of a Torpedo, has 

 been found at Monte Bolca ; and Cyclohatis, from the upper 

 cretaceous limestone of Lebanon, is probably another extinct 

 representative of this family. 



Fourth Family — RAjiDiE. 



Disk broad, rhombic, generally with asperities or spines; 

 tail with a longitudinal fold on each side. The pectoral fins 

 extend to the, snout. No electric organ; no serrated caudal 

 spine. 



Eaja. — Two dorsal fins on the tail, without spine ; tail with 

 a rudimentary caudal fin, or without caudal. Each ventral fin 

 divided into two by a deep notch. Teeth small, obtuse, or 

 pointed. Pectoral fins not extending forwards to the extremity 

 of the snout. Nasal valves separated in the middle, where they 

 are without a free margin (see Fig. ] , p. 34"). 



