SI'l'R-SlIAUKS. 



11. -)7 



fin-spiTies; Echinorhini" with the first dorsal lin oppo- 

 site to the ventrals and witli large dermal spines, si- 

 milar to the aciilii (if the Hays, hut without dorsal tin- 

 spines; and Sjiuim id(i-\ with externally prominent spine 

 het'ore each dorsnl tin. Two of these families ai'e re- 

 presented in. the Scandinavian fauna. 

 .1; At tlie anterior margin of each 



dorsal fin a more or loss prominent 



spiui'. — Pam. Spinacidn-. 



a: Distance between each nostril 



and the tip of the snout oon- 



sidenibly more than half of that 



between the former and the 



moutli S<j>ialii.'< <tr(nillii<i:i. 



h: Distance between each nostril 



and the tip of the snout less 



than half of that between the 



former and the mouth Etmopterus njiina.r. 



B: Ko externally prominent dorsal fin- 

 spines. — Fam. Scymiddcv Acauthorhinxis rurrltarias. 



Fam. SPINACID^. 



Skin ttniformlif slnK/ireued. First dorsnJ fi)i set Iialf- 

 rciitrals or fiirtlier for/card. At the anterior margin 



The intermediate position between the (_"ow-Sharks 

 {Notidanid(c) and the Roussettes {SryUiida) occupied in 

 many respects by the VijclospondijU, is especially mani- 

 fested in the form of the jaw-teeth. The primitive 

 Notidanidan type is characterized partly by the diffe- 

 rence of the teeth in both jaws — longer (broader) and 

 coarser, like serrate disks, in the mandible — partly by 

 the obliquity in the growth of the denticulations, espe- 

 cially in the lateral teeth of the lower jaw, with the 

 tips of all the denticles directed outwards (towards the 

 corners of the mouth) and with the innermost (or one 

 of the innermost) denticles largest, so that the others 

 evidentl)' answer to accessory cusps. In most of the 

 CyclospondijH, and especially within the present family, 



trail lietireen the perpendiculars from the pectorals and 

 of each dorsal Jin a more or less prominent spine. 



this difference between the jaws, as well as the obli- 

 quity of the teeth, has persisted — only one genus, the 

 Greenlandic and Nortli American Centrosci/llium, has 

 teeth similar in both jaws and resembling those of the 

 Roussettes — or the obliquity has advanced yet further, 

 the original inner edge of the largest denticle being 

 turned entirely aside and having become an inci.sive 

 upper edge; and this form of dentition may finally 

 develop not only in the lower jaw but also in the 

 upper. The differences in the dentition besides af- 

 ford the best distinctive characters between tlie .5 

 genera into wliich the family of the Spur-.Sharks 

 has been divided, together including about 20 known 

 species. 



Genus SQUALUS. 



Teeth of the upper and loirer jaws almost similar in form, obliquely shaped incisors. Nostrils middle-sized, their 

 width much less than the distance from the tip of the snout to the middle of a transverse line crossing their an- 

 terior margins. Pectoral fins triangular {following the ordinary Shark type), with the outer posterior margin 



concave. Dorsal fin-spines without lateral grooves. 



In the woi'ks of most recent writers the Linn;T?an ' he employed this generic name, Linnjeus had first in 



generic name of Squalus has been dropped entirely, or view the species which is commonest in Scandinavian 



applied, as in BoxAPAiiXE, to the Blue Sharks, as re- ■ waters, and which he ranged first in his systematic 



presenting the highest development of the Shark type. enumeration of the Sharks. 



.ToRDAN and Gilbert, however, have advanced the opi- Among the Sharks destitute of anal fin the genus 



nion", previously maintained l)y Rafinesqle'*, that, when Squalus is the most differentiated or, so to say, mo- 



" Containing a solit.iry species, Echinorhiiius f:piiiOsus, from tlie Atlantic between the Nortli Sea and tlie Cape of Good Hope and 



from the Mediterranean. 



' Containing the genera Centrophorus, Ventrina, Centrosci/lliurn. Sgualus, and Etmopterus. 



' Bull. U. S. Nat. Mus., No. 16, p. 16. 



■^ Varatt. N. Gen., Spec, p. 13. 



