SELACHOIDEI. 323 



seasons it is gregarious, and many specimens may be seen in 

 calm weather lying together motionless, with the upper part 

 of the back raised above the surface of the water ; a habit 

 from which this Shark has derived its name. The buccal and 

 brancliial cavities are of extraordinary width, and, in conse- 

 quence of the flabby condition of those parts, the head pre- 

 sents a variable and singular appearance in specimens lying- 

 dead on the ground. This peculiarity, as well as the circum- 

 stance that young specimens have a much longer and more 

 pointed snout than adult ones, has led to the erroneous opinion 

 that several different genera and species of Basking Shark 

 occur in the European seas. The brancliial arclies of Sclache 

 are provided with a very broad fringe of long (five to six inches) 

 and thin gill-rakers, possessing the same microscopical struc- 

 ture as the teeth and dermal productions of Sharks. Similar 

 gill-rakers have been found in a fossil state in the Crag of 

 Anvers in Belgium, proving the existence of this Selachian 

 type in the tertiary epoch. Nothing is known of the repro- 

 duction of this fish. The latest contributions to its history 

 are by Steciistrup in " Overs. Dansk. Vidensk, Selsk., For- 

 handl." 1873, and by Favcsi in " Annal. Mus. Civ. Genova," 

 1874 and 1878. 



Third Family — PtHiNODONxiDiE. 



No nictitating membrane. Anal fin present. Two dursal 

 fins, the first nearly opposite to the ventrals, loithout spine in 

 front. Moitth and nostril near the extremity of the snout. 



Tins small family comprises one species only, Bhinodon 

 typicus, a gigantic Shark, which is known to exceed a length 

 of fifty feet, but is stated to attain that of seventy. It does 

 not appear to be rare in the western parts of the Indian 

 Ocean, and possibly occurs also in the Pacific. It is one 

 of the most interesting forms, not unlike the Basking Shark 

 of the Northern Seas, having gill-rakers like that species ; 



