KEY TO THE FAMILIES. XV. 



II, Gills attached, generally with several openings; caudal unsymmetrical or absent. 

 A. One gill opening only. 

 Chlmcerida;. Caudal unsymmetrical ... ... p. 74 



B. Gill openings five to seven. 

 * Gill Openings Lateral (Sharks). 

 f Eye with a nictitating membrane. 



Carcharihke. Two dorsals and an anal ... ... p. 75 



1 1 Eye without nictitating membrane. 



a. An anal fin. 



1. Two dorsal fins. 



Lamnidce. First dorsal between pectorals and ventrals ; teeth 



acute ... ^.. ••- ••• • •• P- 77 



Cestraciontidce. First dorsal between pectorals and ventrals ; 



teeth obtuse ... ... ... ••• p. 80 



ScyllUdce. First dorsal above or behind the ventrals ... p. 79 



2. One dorsal fin. 



Notidan'idce. Dorsal opposite to the anal ... ... p. 78 



b. No anal fin. 



Spinaddce. Two dorsal fins ... ... ... p. 80 



* * Gill Openings Ventral (Eays). 

 ■}- Snout produced. 



EUnohatidce. Two dorsals on the tail ; pectorals not extending 



to the snout ... ••■ ••• ••• p. 82 



Sajidce. Two dorsals on the tail ; pectorals extending to the 



snout ... ... ••• ••• ••• P- S3 



Trygonidoe. Spine on the tail ; pectorals confluent at extremity 

 of snout ... ••• ••• ••• P- 84 



Myliohatidce. Spine on the tail ; snout with a detached pair of 



cephalic fins ... ••• ••• ••• P- §6 



1 1 Snout not produced ; rounded. 



Torpedinidce. Caudal well developed ... ... p. 83 



III. Gills fixed sacs, generally with seven openings ; body eel-like, mouth 



circular, suctorial. 

 Petromyzoutida;. Head without barbels ; fresh water ... p. 86 



Myxinidse. Head with barbels ; marine .. ... p. 87 



IV. Branchial clefts m great number ; mouth a longitudmal fissure with cirri on 



each side. 

 Clrrostomi. Marme ; small ; eye rudimentary ... ... p. 88 



