52 Bulletin 47, United States National Museum. 



Family XVII. RHINODONTID^E. 

 (THE WHALE SHARKS.) 



Origin of the first dorsal fin somewhat in advance of the ventrals; the 

 second small, opposite the anal ; hoth without spines ; a pit at the root of 

 the caudal ; lower lobe of the caudal well developed ; sides of the tail with 

 a keel; no nictitating membrane; spiracles very small ; mouth and nostril 

 near the extremity of the snout ; teeth very small and numerous, conical ; 

 gill openings wide, the last one above the base of the pectorals. Large 

 sharks, of warm seas. Two species are known, Rhinodon typicus, from 

 the Cape of Good Hope, and the following. (RHINODON'TID^E, Giinther, 

 Cat., vin, 396). 



a. Teeth each recurved backward and acutely pointed, swollen, and with a heel-like projec- 

 tion in front rising from its base. MICIUSTODUS, 36. 



36. MICRISTODUS, (Gill). 



Micristodus, GILL, Proc. Ac. Nat. Sci. Phila., 1865, 177, (jwncfoftu). 



This genus is known from its teeth only. These are described as fol- 

 lows : "The teeth are fixed and extremely minute, the largest little more 

 than a line in length (in a shark 20 feet long) and decrease towards the 

 ends of the jaw; they are disposed in regularly transverse rows, of which 

 there are 164 to 167 on each side, while in front there are 13 to 16 in each 

 transverse row; each tooth is recurved backward and acutely pointed, 

 swollen, and with a heel-like projection in front rising from its base." 

 (Gill.) (fiiKfiue, small; tcrrof, an upright projection; oJoi'f, tooth.) 



70. MICRISTODUS PUNCTATUS, Gill. 



A very large shark found in the Gulf of California. No description has 

 been given, and only the teeth are yet known, (punctatus, spotted.) 

 Micristodus punctalus, GILL, Proc. Ac. Nat. Sci. Phila., 1866, 177, Gulf of California. 



Order F. CYCLOSPONDYLI. 

 (THE CYCLOSPONDYLOUS SHARKS.) 



Calcareous lamellae arranged in one or more concentric series or rings 

 about a central axis in each vertebra. Spiracles present. Anal fin want- 

 ing. Dorsal fins 2, with or without spine. As here understood, the order 

 Cyclospondyli includes the sharks of the groups called Cyclospondyli and 

 Tectospondyli by Hasse. The vertebrae in the rays show similar structures, 

 and it is probably from sharks of this group that the Batoidei are de- 

 scended. (ffvicAo;, circle; aTrovdwAof, vertebra.) 



FAMILIES OF CYCLOSPONDYLI. 



a. CYCLOSPONDYLI : Vertebrae with the calcareous lamellae arranged in a ring about the central 

 axis. Pectoral fins normal, not expanded or deeply notched. Anal fin absent ; spiracles 

 preeent ; no nictitating membrane ; gill openings before pectorals; caudal bent upward, 

 the lower lobe little developed. 



6. Dorsal fins each provided with a stout spine, the first dorsal far in advance of ventrals. 



SQUALID^E, xvm. 



