1 4 Memoir Sears Foundation for Marine Research 



species with a well developed caudal fin (with cartilaginous radials) but others without 

 one; fins without horny rays (ceratotrichia) ; in most species a strong serrated tail spine 

 (or spines). This group includes the so-called Sting and Whip Rays, Butterfly Rays, 

 Eagle Rays, and Devil Rays. 



The dividing lines that separate the torpedinoids, the rhinobatoids, and the 

 pristoids from the other suborders are sharp. But the gap between the rajoids and 

 myliobatoids is partially bridged by one group, Anacanthobatidae (p. 327), in which 

 the margins of the pelvics are as deeply notched as in most of the Rajoidea but in 

 which the tail is diagnostic in that it is whip-like, without trace of a dorsal fin. It is 

 classed here among the Rajoidea, but as a separate family (p. 327) because of its pelvics. 



Number of Genera and Species. On the basis of present knowledge, the living 

 representatives of the five suborders of batoids appear to be divisible into 16 families 

 and about 47 genera. At present about 300—340 recognizable species have been de- 

 scribed. A critical comparison of representatives of closely allied forms from different 

 ocean areas doubtless will result in some condensation. But our own experience with 

 the genera Breviraja (p. 284) and Cruriraja (p. 313) suggests that any reductions so 

 caused will be more than counterbalanced by the discovery of new species from regions 

 where the batoid fauna has been studied only casually, especially from the deeper levels 

 along the continental slopes. 



Key to Suborders 



I a. Snout much prolonged as a flat narrow blade, its either edge armed with a single 



series of large tooth-like structures; radial cartilages of pectoral and pelvic fins 



supplemented distally by much more numerous fine horny rays, their inner ends 



embracing the outer ends of the cartilaginous radials. Pristoidea, p. 15. 



lb. Snout not prolonged as a blade-like structure, its edges without teeth. 



2 a. Cranial support of anterior margin of disc consisting of a preorbital cartilage 

 on either side, expanded forward, variously branched or reticulate (easily felt 

 even in large specimens, though not visible externally), with one or two 

 rostral elements also branched in some; skin of disc as well as of tail wholly 

 naked in most species;^* a highly developed electric organ on either side 

 between head and forward extension of pectoral, often visible externally; tips 

 of branchial rays expanded as rounded plates. Torpedinoidea, p. 80. 



2 b. A single rostral cartilage as a cranial support for anterior margin of head 

 either present or not; electric organs, if any, rudimentary, on tail; skin in most 

 species with scales, thorns, or spines; tips of branchial rays but little ex- 

 panded, if at all. 



3 a. Tail sector so stout that it is not marked off definitely from body sec- 

 tor; dorsal and caudal fins well developed, supported distally by horny 

 rays, basally by the cartilaginous radials. Rhinobatoidea, p. 43. 



26. Described as having partly spinous papillae in one species (p. 92). 



