FISHES OF THE GULF OF MAINE 17 



5. Gill openings very large, the first pair nearly meeting below the throat; teeth tiny, many hundred in number; gill 



arches with numerous horny gill rakers directed inward-rearward Basking shark, p. 28 



Gill openings, confined to sides of head; teeth large, few in number; gill arches do not have horny gill rakers 6 



6. Upper teeth broadly triangular, with serrate edges; anal fin is entirely behind second dorsal fin 



White shark, maneater, p. 25 



Upper teeth with smooth-edged cusp, with or without a denticle on either side, at the base; anal fin is not entirely 



behind second dorsal fin 7 



7. First two teeth from center in each jaw are similar to the succeeding teeth; origin of first dorsal fin is over or in front 



of inner corner of pectoral fin when latter is laid back ; forward part of caudal fin has a small secondary lateral keel 

 on each side, below the primary keel formed by the lateral expansion of the caudal peduncle. 



Mackerel shark, p. 20 



First two teeth from center in each jaw are noticeably more slender and more flexuous than the succeeding teeth; 



origin of first dorsal fin is behind inner corner of pectoral fin when latter is laid back; forward part of caudal fin does 



not have a secondary longitudinal keel Sharp-nosed mackerel shark, mako, p. 23 



8. Upper lobe of caudal fin is nearly or quite as long as head and body combined Thresher, p. 32 



Upper lobe of caudal is less than one-half as long as head body combined 9 



9. Second dorsal fin is nearly as high vertically as first dorsal fin 10 



Second dorsal fin is less than one-half as high vertically as first dorsal fin 12 



10. First dorsal fin is wholly or mostly forward of the origin of the pelvic fins 11 



First dorsal fin is wholly posterior to bases of pelvic fins Chain dogfish, p. 34 



11. Teeth high, narrow, sharp pointed, not in mosaic arrangement; snout conical; fifth gill openings well in front of 



pectoral fins Sand shark, p. 18 



Teeth small, low, rounded, in mosaic arrangement; snout flat, broadly rounded in front; fifth gill openings are behind 

 origins of pectoral fins Smooth dogfish, p. 34 



12. Origin of first dorsal fin far behind inner corner of pectoral fin; upper surface brilliant blue in life. 



Blue shark, p. 38 



Origin of first dorsal fin is over or anterior to inner corners of pectorals; ground color of upper surface is gray, brownish 



or dusky in life, not bright blue 13 



13. Length of snout in front of mouth is not more than one-half as great as breadth of mouth; upper jaw has a furrow 



on either side extending from outer corner forward past level of eye; caudal peduncle with a low longitudinal keel 

 on either side; upper and lower teeth are of shapes shown in figure 11; their margins coarsely serrate. 



Tiger shark, p. 37 



Length of snout in front of mouth is more than two-thirds as gref t as breadth of mouth; furrows on upper jaw, if 



any, do not extend forward-inward as far as level of eye; caudal peduncle without longitudinal ridges; teeth are 



not of shape shown in figure 11, their margins either only very finely serrate or smooth 14 



14. Outer corners of mouth have a short "labial furrow" extending inward-forward along each jaw; teeth are alike in 



the two jaws, directed sharply outward, margins of upper teeth smooth, as well as those of lower teeth. 



Sharp-nosed shark, p. 40 

 Outer corners of mouth have no labial furrow on lower jaw and upper labial furrow is so short as to be hardly notice- 

 able; teeth directed only moderately outward, their margins only finely serrate; lowers noticeably more slender 

 than uppers 15 



15. Origin of first dorsal fin is about over inner corner of pectoral when latter is laid back; vertical height of first 



dorsal fin is less than distance from eye to first gill opening Dusky shark, p. 41 



Origin of first dorsal is about over axil (armpit) of pectoral, its vertical height (after birth) is at least as great as 

 distance from eye to third gill opening Brown shark, p. 43 



16. Trunk much flattened dorso-ventrally; eyes on top of head; front margins of pectorals overlap the gill openings. 



Angel shark, note, p. 18 

 Trunk subcylindrical; eyes on side of head; front margins of pectorals do not overlap the gill openings 17 



17. Each dorsal fin is preceded by a stout and conspicuous spine 18 



Doisal fin-spines either lacking, or are so nearly concealed in the skin that their presence can be detected by touch 



only 20 



18. Upper teeth with 5 erect cusps; lower teeth with only one cusp, the successive cusps directed outward, forming a 



nearly continuous horizontal cutting edge all along the jaw Etmopterus princeps, p. 47 



Upper and lower teeth are alike in shape 10 



19. Upper teeth quadrangular as well as lower teeth, with one cusp directed outward, forming a nearly continuous 



horizontal cutting edge along each jaw Spiny dogfish, p. 47 



Upper and also lower teeth each have 3 to 5 erect, triangular cusps Black dogfish, p. 51 



20. First dorsal fin well in advance of pelvic fins; upper teeth noticeably different in shape from lower teeth 21 



First dorsal fin stands over posterior part of bases of pelvic fins; upper are teeth similar to lower teeth in shape. 



Bramble shark, d. 56 



