SYNOPSIS OF THE ARRANGEMENT OF FISHES. 191 



Order III. CARTILAGINES. 



Skeleton cartilaginous; branchial apertures resembling slits in 

 the skin ; head wide and flattened ; pectorals very large. 



Family 1. SQUALIDiE. Sharks 

 Body pisciform ; all the fins distinct. 



1 . Sub-family Squalin^. — No spiracles behind the eyes, or 



very minute ones in the aberrant genera. 



Squalus. Teeth compressed, pointed, the sides serrated. 



Squalus. Teeth serrated on each side ; tail rather short. 

 Alopias. Posterior dorsal adipose ; tail oblique, very long. 

 Serictius. Head with two horn-like appendages. 



Dalatias. No spiracles ; anal fin wanting ; dorsal fins two, 

 armed with spines. 



Lamna. Spiracles sometiines minute ; caudal fin large, lu- 

 nate ; mouth beneath. 



Selaclius. Teeth very small, narrow and conic ; ntiuzzle short. 

 Isurus. No spiracles ; snout lengthened, acute ; tail keeled. 

 Lamna. Spiracles minute; snout pyramidical ; tail keeled. 

 Alopecias* Spiracles minute; teeth simply triangular; upper 

 caudal lobe extremely long. 



Rhineodon. Spiracles minute ; teeth very small, acute ; mouth 

 terminal ; caudal lunate ; tail keeled. 



2. Sub-family Centrinin.^. — Spiracles behind the eyes ; 



dorsal fins sometimes spined. 



Centrixa. No anal fin ; dorsal fins two, armed with spines. 



Spinax. Dorsal spines in front of the fins ; body smooth. 

 Eimopterus. Resembling Spinax, but .with only three branchial 



apertures. 

 Centrina. Dorsal spines in the middle of the fins. 

 Cerdrophorus. Body armed with hard scales or prickles. 



Galeus. Dorsals two ; anal one ; tail unequal, oblique ; 



teeth as in Squalus. 



Galeus- Spiracles rather large ; tail without a dimple. 

 Galeocerdo. Spiracles small ; a dimple at the base of the tail. 



ScTLLiuM. Spiracles large ; caudal fin irregular, lobed, with 

 the tip truncate. 



Pristiurus. Snout lengthened ; base of the tail serrated with scales. 

 Chlloscyllium. Under lip broad, membranaceous j upper nasal valve 

 cirrated. 



* The two sub-genera yi/opas and JZo;jm«5 require investigation. Are 

 they the same ? or do they represent each other ? 



