SPUR-SIIARKS. 
1157 
fin-spines; Echinorhini a with the first dorsal fin oppo- 
site to the ventrals and with large dermal spines, si- 
milar to the aculei of the Rays, but without dorsal fin- 
spines; and Spinacidce b , with externally prominent spine 
before each dorsal fin. Two of these families are re- 
presented in the Scandinavian fauna. 
A : At the anterior margin of each 
dorsal fin a more or less prominent 
spine. — Fam. Spinacidce. 
a: Distance between each nostril 
and the tip of the snout con- 
siderably more than half of that 
between the former and the 
mouth Squalus acanthias. 
b: Distance between each nostril 
and the tip of the snout less 
than half of that between the 
former and the mouth Etmopterus spinax. 
B: No externally prominent dorsal fin- 
spines. — Fam. Scymnidce Acanthorlrinus carcharias. 
Fam. SPIN AC 11) M. 
First dorsal fin set half-way between the perpendiculars from the pectorals and 
At the anterior margin of each dorsal fin a more or less prominent spine. 
\ 
Skin uniformly shagreened. 
ventrals or further forward. 
The intermediate position between the Cow-Sharks 
(. Notidanidce ) and the Roussettes (Scylliidee) occupied in 
many respects by the Cyclospondyli , 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 
evidently answer to accessory cusps. In most of the 
Cyclospondyli , and especially within the present family, 
this difference between the jaws, as well as the obli- 
quity of the teeth, has persisted — only one genus, the 
Greenlandic and North American Centroscyllium, 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 incisive 
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 the 5 
genera into which the family of the Spur-Sharks 
has been divided, together including about 20 known 
species. 
Genus SQUALUS. 
Teeth of the upper and loiver jaivs 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 works of most recent writers the Linnsean he employed this generic name, Linnaeus had first in 
generic name of Squalus has been dropped entirely, or view the species which is commonest in Scandinavian 
applied, as in Bonaparte, 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. 
Jordan and Gilbert, however, have advanced the opi- Among the Sharks destitute of anal fin the genus 
nion c , previously maintained by Rafinesque* that, when Squalus is the most differentiated or, so to say, mo- 
a Containing a solitary species, Ecliinorhinus spinosus, from the Atlantic between the North Sea and the Cape of Good Hope and 
from the Mediterranean. 
6 Containing the genera Centrophorus , Centrina , Centroscyllium , Squalus , and Etmopterus. 
c Bull. U. S. Nat. Mus., No. 16, p. 16. 
d Caratt. N. Gen., Spec., p. 13. 
