52 Bulletin 47, United States National Museum. 



Family XVII. RHINODONTIDtE. 



(ThK WllALE SlIAKKS.) 



Origin of the first dorsal fiu somewhat in aclvauce of the veutrals; the 

 second small, opposite the anal ; both 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, lihiuodon typicus, from 

 the Cape of Good Hope, and the following. (Rhinodontid.e, Giiuther, 

 Cat., VIII, 396). 



«. Teeth eacli recurved backward and acutely pointed, swoUeu, and with a heel-liko projec- 

 tion in front rising from its base. Micbistoucs, 3G. 



36. MICRISTODUS, (Gill). 



Micrislodus, Gill, Troc. Ac. Nat. Sci. Phila., 1865, 177, {pmn:talns). 



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 wath a heel-like projection in front rising from its base." 

 (Gill.) (//t/cpof, small ; (arof, an upright projection; bdovg, looih..) 



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, {pntictatus, spotted.) 



MicrislodtKS pmictalun. Gill, Proc. Ac. Nat. Sci. Phila., 1865, 177, Gulf of California. 



Order F. CYCLOSPONDYLI. 

 (The Cyclospondylous Sharks.) 



Calcareous lamellie arranged in one or more concentric series or rings 

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

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

 Cycloapornhjli includes the sharks of the groups called Cydosponihjli and 

 Tecionpnndyli by Hasse. The vertebra- in the rays show similar structures, 

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

 scended. (KiiK/lof, circle ; anovih'htr, xevtGhra.) 



Families of Cyclospondyli. 



a. CvciospoNDYLi : Vcrtebr.i; with the calcareous lamelhe arranged in a ring about tlie central 



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



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



the lower lobe little developed. 



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



SQUALtDJi, XVII I. 



