1 2 Memoir Sears Foundation for Marine Research 



hyperborea, p. 206) is known to find a congenial home regularly in water colder than 

 0° C (32° F), and perhaps a second species (R. spinicauda, p. 271). 



As a whole the batoids constitute a salt-water group, but several species of Sting 

 Rays (family Potamotrygonidae, p. 334) have colonized fresh water in the lower reaches 

 of South American rivers that drain into the Atlantic (p. 334). Sawfishes are also found 

 regularly in fresh water and are even landlocked. 



Geological History. The Guitarfishes (Rhinobatidae), which are intermediate in 

 form between the more highly specialized groups of Rays and the Sharks, were in 

 existence in the Upper Jurassic. Thus the oldest batoids were more recent in their 

 geological appearance than the oldest of the groups of Sharks that exist today, ^^ and 

 they were far more recent than some extinct groups of Sharks. The Sawfishes (Pristidae), 

 the Skates (Rajidae), and the Sting and Eagle Rays (Dasyatidae, Myliobatidae) ap- 

 peared in the Cretaceous, the Torpedo Rays in the Eocene, and teeth identifiable as 

 those of a Devil Ray, closely allied to the modern Manta, are known from the Pliocene. 2* 



Classification. Scientific opinion is now tolerably crystallized as to the basic group- 

 ing of the batoids, though the taxonomic systems that have been proposed by different 

 students during the last half century have differed widely as to the number of sub- 

 divisions recognized and as to the names employed for the groups above the grade of 

 family. 25 



Beginning with the Electric Rays: these are sharply set apart from all other 

 batoids by the possession of highly developed electric organs in the anterior part of 

 the body, by the greatly expanded antorbital cartilages that support the anterior margin 

 of the disc, by the peculiar branched rostral cartilage or cartilages, and by the rounded 

 plate-like terminations of the slender branchial cartilages. We follow common usage 



23. The Port Jackson Sharks (Heterodontidae) date back to the Lower Jurassic, the Six-gilled Sharks (Hexanchidae) 

 to the Middle Jurassic. 



24. See Romer (Vert. Palaeont., 2nd ed., 1945: 577) for a list of the geological horizons from which batoid remains 

 of the various families and genera have been reported. 



25. This diversity of opinion may be illustrated by the following examples: Regan (Free. zool. Soc. Lond., 1906: 723- 

 724); regarding the batoids only as a suborder (Hypotremata), proposed two "Divisions," the Narcobatoidei with 

 one family for the Electric Rays, the Batoidei with two families for all other batoids. But later (Encyc. Brit., 24, 

 191 1 : 596) he recognized seven families. Garman (Mem. Harv. Mus. comp. Zool., 36, 1913: 257, 258), who classed 

 them as a "division" of the Chondropterygia, defined six "Groups of Families" (Rhinobatoidei, Narcoidei, Raioidei, 

 Dasybatoidei, Myloidei, and Mobuloidei). Jordan (Class. Fish., Stanford Univ. Publ. Biol., 3 [2], 1923: 102) di- 

 vided the order Batoidei into three suborders: Sarcura with five modern families for the Saw- and Guitar-fishes 

 and for the Skates, Narcaciontes with one family for the Electric Rays, and Masticura with five modern families 

 for the Sting, Butterfly, Eagle, Cow-nosed, and Devil Rays. Bertin (Bull. Inst, oceanogr. Monaco, 775, 1939: 19) 

 includes all modern Elasmobranchs in a single order, Euselachii, distributing the Skates, Rays, and Sawfishes among 

 four suborders (Squatinorajiformes, Rajiformes, Torpediformes, and Trygoniformes) with seven families, the 

 modern Sharks among seven suborders. Fowler (Bull. U. S. nat. Mus., 100 [jj], 1941: 2S9-290) has classed the 

 batoids as an order (Rajae) with four primary subdivisions (Rhinobatoidei, Torpedoidei, Rajoidei, and Mylio- 

 batoidei). Beebe and Tee-Van (Zoologica N. Y., 26, 1941: 245) treat the batoids as a "super order" (Platosomeae) 

 consisting of two orders: Narcobatea, with one family, for the Electric Rays; and Batea, with three "superfamilies," 

 Rhinobatoidea, Rajoidea, and Dasybatoidea, each having two, one, and four families respectively. Fowler has 

 recently followed them in ranking the batoids as a superorder, though he has given them the name Rajioidea (Notul. 

 Natur. Acad. nat. Sci. Philad., 187, 1947: 13). Finally, Berg, in his Classification of Fishes (Trav. Inst. Zool. Acad. 

 Sci. URSS, 5 [2], 1940, and lithoprinted ed. 1947: 139 [Russ.], 381 [Eng.]), classes the batoids as an order, Raji- 

 formes, which is divided directly into eight modern families and one fossil family, without the intermediary of any 

 suborders. 



