152 SUB-CLASS ELASMOBRANCHII. 



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Australia, 36 ft. ; Odontaspis L. Ag., temp, and trop. seas ; Alopecias 

 (Alopias) M. and H., teeth triangular, flat, smooth edges, caudal fin 

 long, no keel at side of tail, temp, and trop. seas ; A. vulpes Gmelin, 

 thrasher-shark, fox ; Selache Cuv. (Cetorhinus Blainv.), teeth small, 

 numerous, conical and smooth, keel at side of tail, whalebone-like gill- 

 rakers consisting of dentine on the gill-arches, Arctic to Med. ; S. maxi- 

 mus Gunner, basking-shark, sun-fish, one of the largest of living fishes, 

 to 40 ft., large gill apertures, vertebrae appear to be tectospondylous, 

 owing to presence of a number of concentric lamellae in the adult ; in- 

 offensive, of great strength, has been known to tow a 70-ton boat against 

 a fresh gale ; a large fish yields 1 tons of oil ; Pseudotriacis Capello. 

 Mitsukurina Jordan (Scapanorhynchus S. Wood), Japan. Extinct 

 genera : Orthacodus S. Wood, Jurassic and Cretaceous ; Odontaspis 

 Ag., Upper Cretaceous. 



Fam. 7. Rhinodontidae. Whale-sharks ; asterospondylous ; origin 

 of first dorsai fin in front of pelvic ; the second small, opposite the anal, 

 both without spines ; a pit at root of caudal ; side of tail with keel ; 

 spiracle small ; membrana nic titans absent ; mouth and nostril near the 

 front of snout ; teeth small ; gill openings wide, with gill-rakers, Cape of 

 Good Hope, Seychelles, Japan. Rhinodon Smith ; a gigantic shark known 

 to exceed 50 ft., said to attain 70 ft. 



Fam. 8. Spinacidae. Cyclospondylous ; spiracles present ; gill 

 openings narrow ; without nictitating membrane ; a deep groove along 

 either side of the mouth ; a spine on front side of each dorsal fin ; without 

 anal fin. Centrina Cuv. (Oxynotus Raf.), body somewhat three-sided 

 with a fold of skin at each angle, teeth in lower jaw triangular, erect and 

 with finely serrated edges, no membrana met., Med. and adjacent At- 

 lantic ; C. Salviani Risso, attains to 4-5 ft. ; Acanthias Risso (Squalus), 

 teeth rather small, their points placed so obliquely that their inner margin 

 which is smooth forms the cutting edge, no membrana nict., temp, 

 seas of both hemispheres ; A. vulgaris Risso, picked dog-fish, spur-, spear-, 

 or bone-dog, hoe, skittle-dog ; viviparous ; Centrophorus M. and H. , 

 Eur. seas, Moluccas ; some species live at a great depth (400-500 

 fathoms) ; Scymnodon Boc and Cap. ; Spinax Cuv. (Etmopterus Raf.), 

 Eur. Seas, W. Indies ; Centroscyllium M. and H., Greenland, has been 

 taken 300-400 fathoms. 



Fam. 9. Scymnidae. Like Spinacidae, but no spines on dorsal fins ; 

 Scymnus Cuv., Med. and Atlantic ; Laemargus M. and H. (Somniosus 

 Lie Sueur), teeth in upper jaw small and conical, those in lower jaw in several 

 rows, their points placed so obliquely that their inner margin, which is 

 smooth, forms the cutting edge ; L. microcephalies Kroyer (borealis M. and 

 H.), Greenland shark; notochordal sheath imperfectly segmented, un- 

 calcified (calcified and segmented in L. rostratus) ; attains 25 ft., bites 

 pieces out of whales ; with two pyloric caeca ; eggs large, soft, globular, 

 without shell, dropped in the ooze on the sea bottom, said to be fertilised 

 externally; they breed at considerable depths (100 fathoms); Euproto- 

 micrus Gill, Ind. Ocean ; Echinorhimis Blainv., skin with irregularly 

 placed round osseous tubercles, teeth large, oblique, with several small 

 cusps on each side of the main one, Med. and Atl., E. spinosus Blainv., 

 to 8 ft. ; Isistius Gill. 



Fam. 10. Rhinidae. Ray-like sharks. Tectospoiidylous ; spiracles 

 large, gill openings wide, lateral, and partly concealed from above by 

 pectoral fins ; body flat ; mouth anterior ; nostrils at front end of snout 



