450 Memoir Sears Foundation for Marine Research 



with I to several radial elements} pelvics transverse; heart valves in 2 to 4 rows. Develop- 

 ment usually ovoviviparous, but probably oviparous in some cases. 



Key to Families 



la. Each dorsal fin preceded by a long or short spine with tip exposed or concealed.^ 



Squalidae, p. 450. 

 lb. Second dorsal fin, and usually the ist, without a spine.^ 



2a. Teeth with only i cuspj uppers and lowers unlike, the former narrow, raptorial, 

 the latter expanded widely laterally as a cutting edge (sectorial). 



Dalatiidae, p. 499. 

 2b. Teeth with several cusps, uppers and lowers similar, sectorial. 



Echinorhinidae, p. 526. 



Family SQUALIDAE 



Characters. Squaloidea with a spine in each dorsal fin, long in some cases but so short 

 in others as to be easily overlooked; teeth with i or several cusps, alike or unlike in the 2 

 jaws. Characters otherwise those of the suborder. 



Genera. Generic distribution of the various members of this family is still in some 

 confusion owing to the fact that all the characters that have been regarded as generically 

 diagnostic by one author or another are intergrading, not strictly alternative. Conse- 

 quently, the accompanying Key is necessarily tentative. 



Tentative Key to Genera 



I a. Fin spines originating about at midpoint of bases of dorsal fins and running forward 

 to emerge from anterior margins of latter; trunk very stout, sub triangular, with longi- 

 tudinal dermal ridges anterior to pelvic fins. Oxynotus^ Rafinesque, 1 8 lO. 



Eastern Atlantic, Mediterranean, 

 Australian region. 

 lb. Fin spines originating at origins of dorsal fins and lying along anterior margins of 

 latter; trunk slender, subcylindrical, with dermal longitudinal ridges (if any) con- 

 fined to sector posterior to pelvic fins. 

 2a. Upper teeth with several cusps. 

 3a. Teeth similar in the 2 jaws. 



Centroscyllium Miiller and Henle, 1841, p. 480. 

 3b. Upper and lower teeth noticeably unlike, the lower with only i cusp. 



Etmofterus Rafinesque, 18 10, p. 487. 



1. Even in the genera in which the spines are shortest (e.g., Centroscymnus, p. 493) they are easily detected by 

 touch. 



2. In Euprotomicrus the first dorsal may or may not have a spine. 



3. Classed as a separate family (Oxynotidae) by some authors. 



