RHYNCHOBATUS.--Dorsal fins without spine, the first opposite to the ventrals. Caudal fin with the lower lobe well developed. Teeth obtuse, granular, the dental surfaces of the jaws being undulated. [Illustration: Fig. 125.--Dentition of _Rhynchobatus_.] Two species, _Rh. ancylostomus_ and _Rh. djeddensis_, are very common on the tropical coasts of the Indian Ocean. They feed on hard-shelled animals, and attain scarcely a length of 8 feet. RHINOBATUS.--Cranial cartilage produced into a long rostral process, the space between the process and pectoral fin being filled by a membrane. Teeth obtuse, with an indistinct transverse ridge. Dorsal fins without spine, both at a great distance behind the ventral fins. Caudal fin without lower lobe. Numerous on the coasts of tropical and sub-tropical seas; about twelve species. _Trygonorhina_ is an allied genus from South Australia. The oolitic genus _Spathobatis_ is scarcely distinct from _Rhinobatus_; and another fossil from Mount Lebanon has been actually referred to this latter genus. _Trigorhina_ from Monte Postale must be placed here. THIRD FAMILY--TORPEDINIDÆ. _The trunk is a broad, smooth disk. Tail with a longitudinal fold on each side; a rayed dorsal fin is generally, and a caudal always, present. Anterior nasal valves confluent into a quadrangular lobe. An electric organ composed of vertical hexagonal prisms between the pectoral fins and the head._ “Electric Rays.” The electric organs with which these fishes are armed are large, flat, uniform bodies, lying one on each side of the head, bounded behind by the scapular arch, and laterally by the anterior crescentic tips of the pectoral fins. They consist of an assemblage of vertical hexagonal prisms, whose ends are in contact with the integuments above and below; and each prism is subdivided by delicate transverse septa, forming cells, filled with a clear, trembling, jelly-like fluid, and lined within by an epithelium of nucleated corpuscles. Between this epithelium and the transverse septa and walls of the prism there is a layer of tissue on which the terminations of the nerves and vessels ramify. Hunter counted 470 prisms in each battery of _Torpedo marmorata_, and demonstrated the enormous supply of nervous matter which they receive. Each organ receives one branch of the Trigeminal nerve and four branches of the Vagus, the former, and the three anterior branches of the latter, being each as thick as the spinal chord (electric lobes). The fish gives the electric shock voluntarily, when it is excited to do so in self-defence or intends to stun or to kill its prey; but to receive the shock the object must complete the galvanic circuit by communicating with the fish at two distinct points, either directly or through the medium of some conducting body. If an insulated frog’s leg touches the fish by the end of the nerve only, no muscular contractions ensue on the