4. SCYMNID.E. 13 



and skates differ much from each other in appearance ; but intermediate 

 forms connect the two groups closely. The position of the gill-openings 

 is almost the only constantly diagnostic character. (Suborder Sclachoi- 

 dei Giinther, viii, 353-433.) (Latin, squalus, a shark, from the Greek 

 fa/lew T, a shark, which conies from yaA6j, a weasel, or other musteline 

 animal, from resemblances in habits.) 



ANALYSIS OF THE FAMILIES OF SQUALL 



* Pectoral fins moderate, without deep notch at the base in front, 

 t Anal fin absent. 



a. Dorsal fins without spine Sc YMNIDJE, 4. 



aa. Dorsal fins each preceded by a stout spine (rarely concealed in the skin). 



SPIN ACID J3, 5. 

 tt Anal fin present. 

 fc. Dorsal fins two. 

 c. Dorsal fins both without spine. 



d. First dorsal fin behind the veutrals GINGLYMOSTOMATID^E, 6. 



dd. First dorsal entirely in advance of the ventrals. 



e. Caudal fin not lunate, its upper lobe many times longer than the lower, 



with a notch below toward its tip ; tail not keeled. 

 /. Last gill-opening above the base of the pectoral. 



g. Tail moderately developed, forming less than one-third of the total 

 length; eyes with nictitating membranes. 



Ti. Head normally formed GALEORHINID.E, 7. 



lilt. Head hammer-shaped or kidney-shaped by the extension of its 



sides SPHYRXLTXE, 8. 



gg. Tail exceedingly long, forming about half the total length ; eyes 



without nictitating membranes ALOPIIIXE, 9. 



ff. Last gill-opening entirely in front of the pectoral. CARCHARIID^E, 10. 

 ee. Caudal fin lunate ; caudal peduncle with a keel on each side, 

 i. Last gill-opening entirely in front of ventrals. 



j. Gill-openings moderate ; teeth well developed . LAMNIDJE, 11. 

 jj. Gill-openings very large, nearly meeting under the throat; 



teeth small CETORHINID^E, 12. 



ii. Last gill-opening above the base of the pectoral. 



KHINODONTID.E, 13 



ec. Dorsal fins each armed with a stout spine HETERODONTID^E, 14 



bb. Dorsal fin single ; the first dorsal obsolete ; gill-openings 6 or 7. 



HEXANCHID.E, 15. 



* Pectoral fins very large, expanded at the base in front, this expansion separated 



from the neck by a deep notch ; no anal fin . SQUATINID^E, 16. 



SUPBE-PAMILT SCYMNOIDEA. 



(The Scymnoid Sharks.) 



FAMILY IV. SCYMNID^E. ' 



(The Sleeper Sharks.) 



Sharks with two dorsal fins, both icitliout spine, and no anal fin; fins 

 all small ; gill-openings small, entirely in advance of pectorals j mouth 



