44 Memoir Sears Foundation for Marine Research 



dorsal fins on tail, conformation of anterior margin of nostril, and relationship of nostrils 

 to mouth. Some recent authors, in fact, unite all of them in a single family, Rhino- 

 batidae.* They can be grouped in two families, however, according to the shape of 

 the caudal, including the degree of elevation of its axis, and according to the position 

 of the dorsal fins relative to the pelvics. 



Key to Families 



I a. Caudal fin conspicuously bilobed, more or less lunate in form, both lobes sharp- 

 pointed; axis of caudal fin bent upward to a moderate degree; posterior edges of 

 pectorals considerably anterior to origin of pelvics; origin of first dorsal over or 

 a little anterior to bases of pelvics. Rhynchobatidae,* p. 44. 



lb. Caudal fin not bilobed, its axis bent upward only very little, if at all; posterior 

 edges of pectorals extending rearward as far as origin of pelvics or farther; origin 

 of first dorsal considerably posterior to posterior tips of pelvics. 



Rhinobatidae, p. 46. 



Family RHYNCHOBATIDAE 



Characters. General shape intermediate between shark-like and typical ray-like, 

 only moderately flattened; tail sector not marked off from body sector. Snout not pro- 

 duced as a blade, ranging in different genera from short and broadly rounded to wedge- 



FiGURE 7. Rhynchobatus djiddensis. Caudal fin of male, 

 480 mm long, from Ceylon (Harv. Mus. Comp. ZooL, 

 No. 806), about 0.8 X. 



shaped and elongate; no teeth on margins of snout. Posterior corners of pectorals 

 considerably anterior to origin of pelvics. Origin of first dorsal ranging from about over 

 midpoint of bases of pelvics to a little anterior to origins of latter. Caudal fin definitely 



4. Norman, Proc. zool. Soc. Lond., 1926: 941; Berlin, Bull. Inst, oceanogr. Monaco, 775, 1939: 19. 



5. Jordan (Class. Fish., Stanford Univ. Publ. Biol., j [2], 1923: 102) used the name Rhinidae for this family (derived 

 from Rhina Bloch and Schneider 1801, see p. 45). But doing so is likely to lead to confusion, because Rhina has 

 been used many times as the generic name of the squatinoid Sharks, though incorrectly so. 



