20 SELACHII: RAI.9E. — V. 



expanded pectoral fins. The tail is comparatively slender, and its 

 fins are small. Spiracles present. The Rajidm produce large eggs, 

 enclosed in leathery cases; most of the other Pi,aim are ovovi- 

 viparous, bringing forth their young alive. 



Families of Baise. 



(I. Tail comparatively thick, -with two dorsal fins; no serrated caudal spiDs 

 nor cephalic fins. , 

 b. Snout much produced, flat, armed with strong teeth on each side, se( 

 at right angles to its axis ; body somewhat shark-like, the disk grad- 

 ually passing into the tail Peistidid^, 13, 



bb. Snout not saw-like; disk ending abruptly at base of tail, 

 c. Electric organs wanting; skin not perfectly smooth. . Eajid^, 14 

 cc. Electric organs present; a structure of honeycomb-like tubes between 

 pectoral fins and head ; skin perfectly smooth. . Tohpedinid^, 14. 

 aa. Tail slender, with but one dorsal fin or none, and usually armed with a 

 serrated spine. 

 d. Pectoral fins uninterrupted, confluent about the snout; teeth small. 



DASTATID.-E, 15, 



dd. Pectoral fins divided, .leaving detached appendages (" cephalic fins "] 

 on the snout. 



e. Teeth very large, flat, tessellated Aetobatid^, 16, 



ee. Teeth very small, fiat or tubercular ; size enormous, largest of the rays, 



Mantid*, 17, 



Family XIII. PRISTIDID^. (The Saw-fishes.) 



Rays v?ith elongate body, stout, thick tail, and a long saw-like 

 snout, below which is the inferior mouth vrith small blunt teeth. 

 Dorsals and caudal well developed. One genus, with 5 or 6 species. 

 in warm seas. 



19. FRISTIS Latham. (jrpla-Tris, one who saws ; the ancient 

 name.) 



24. P. pectinatus Latham. Saw-fish. Saw with 25 to 28 

 pairs of spines. L. 10 feet. West Indies; occasional N. (Lat., 

 comb-toothed.) 



Family XIV. RAJID^. (The Skates.) 



Rays with the disk broad, rhombic, more or less rough; the 

 males usually with about two rows of strong spines on each pec- 

 toral ; tail rather stout, with a fold of skin on each side, and twc 

 dorsal fins above ; caudal fin small or obsolete ; no serrated spine 

 no electric organs. Egg in a large leathery case, four-angled, and 

 having two tubular horns at each end. Genera 4, species 40 

 mostly of the Northern seas. 



a. Caudal fin rudimentary; pectorals not confluent, leaving u translucen 

 area at the snout; ventrals deeply notched. ... . Raja 20 



