FISHES OF THE GULF OF MAINE 23 



KEY TO GULF OF MAINE SHARKS 



1. Head hammer-shaped Hammerhead, p. 31 



Head of ordinary shape; rounded or pointed nose 2 



2. Only one dorsal fin; six gill slits on each side; body eel-shaped Eel shark, p. 24 



Two dorsal fins (the second may be small but is always perfectly distinct) ; only 5 gill 



slits; body of ordinary shark form 3 



3. Both dorsal fins have spines at their forward margins; no anal fin 4 



Dorsal fins lack spines ° 



4. Rear margin of upper lobe of tail not notched; a very common species 



Spiny dogfish, p. 44 



Rear margin of upper lobe of tail notched near the tip 5 



5. Dorsal spines so small they are hardly visible, though easily felt 



Portuguese shark (Centroscymnus coslolepis) , p. 51 

 Both dorsal spines large Black dogfish, p. 53 



6. There is no anal fin, the paired ventrals being the only fins on the ventral surface 7 



Anal fin present ° 



7. First dorsal fin situated about midway between pectorals and ventrals 



Greenland shark, p. 53 



First dorsal far back as ventrals Bramble shark (Echinorhinus brucus), p. 55 



8. No lateral keels on caudal peduncle (root of tail) ; upper lobe of caudal fin much longer 



than lower " 



A longitudinal keel on either side of caudal peduncle; lower lobe of tail more nearly as 

 large as upper, suggesting tail of a swordfish 14 



9. Upper lobe of caudal fin nearly, if not quite, as long as head and body together 



Thresher, p. 32 



Caudal fin less than half as long as head and body combined 10 



10. Second dorsal at least half as high as first 11 



Second dorsal less than half as high as first 12 



11. Second dorsal considerably smaller than first; teeth small, blunt, and arranged like 



a pavement Smooth dogfish, p. 24 



Second dorsal about as large as first; teeth narrow and pointed Sand shark, p. 34 



12. Origin of first dorsal hardly behind pectorals; upper and lower teeth alike; skin 



spotted Tiger shark, p. 27 



First dorsal originates well behind the pectoials; upper teeth broader than lower; skin 

 not spotted 13 



13. The first dorsal originates about over the inner corner of the pectorals when these are 



laid back; snout broadly rounded Dusky shark," p. 29 



First dorsal originates far behind inner corner of pectoral; snout long and pointed — 

 Blue shark, p. 28 



14. Gill slits very long; first pair nearly meeting on throat; gills with rakers; teeth tiny.. 



Basking shark, p. 41 



Gill slits short, confined to sides of neck; no gill rakers; teeth large 15 



15. Teeth broad, triangular, with serrate edges; second dorsal fin well forward of anal 



White shark, p. 39 



Teeth slender, smooth-edged; second dorsal fin over or hardly in front of anal 16 



16. First dorsal fin originates above axil (armpit) of pectoral 



Mackerel shark (Isurus punctatus), p. 36 



First dorsal fin originates well behind the axil f pectoral 



Sharp-nosed mackerel shark (/. tigris), p. 38 



i« The brown shark (Carcharinus milberti), very abundant west and south of Cape Cod but not yet known from the Gulf, 

 is easily distinguished from its close relative, the dusky shark, by its very tall dorsal An. 



