1128 
SCANDINAVIAN FISHES. 
(12 — 13) does not extend beyond the branchial aper- 
tures, sometimes not even to them, and that the man- 
dibular branch is continuous with this canal. 
In Scandinavian waters Sharks are less common 
and consequently less known and feared than in more 
temperate or tropical seas. About one hundred and 
fifty species are recognised, but of these only eleven 
can be claimed for the Scandinavian fauna. 
In the sketch given by Hasse" of the evolution of 
the Elasmobranchs one group, the Palceonotidani, in the 
present age most nearly represented by the Notidanidce b , 
a family foreign to Scandinavia, rank as the primordial 
type both of the Sharks and Rays. Externally this fa- 
mily is characterized by the possession of only one 
dorsal hn, but of six or seven gill-openings. The proofs 
of its primitive nature must be sought, however, in the 
structure of the spinal column, with its undifferentiated 
vertebrae. From the Palceonotidani, according to ITasse, 
three different evolutional series may be traced, 'with a 
calcified double-cone, more or less distinct and of varying 
development, in the centra of the vertebrae. Its deve- 
lopment is most imperfect in the so-called Cyclospon- 
dyli, where it appears merely as a ring of calcification. 
Externally all these Sharks (the family Spinacidce ), with 
their typical form of body, may lie recognised by 
their want of anal fin. In the other two evolutional 
series the double-cone (composed of two more or less 
deeply hollowed cones, confluent at the vertices) is 
generally developed to such a degree that the bodies 
of the vertebrae are fully amphiccelous; but in one of 
them — the so-called Tectospondyli — it consists of 
smooth, concentric layers of calcification, in the other 
— the so-called Aster ospondyli — calcareous rays issue 
radially from the centrum. The Tectospondyli are 
without anal fin, and their series comprises both two 
Shark families foreign to the Scandinavian fauna, the 
Angel-fishes ( Tthinidce ) and the Saw-Sharks ( Pristiopho - 
ridce), which are transitional even in their external 
form to the Batoidei, and the whole phalanx of the 
Rays. All the remaining Sharks — all furnished with 
anal fin and two dorsal fins — are Asterospondyli , 
and in this series the Plagiostomous type has attained 
its richest development, with the greatest wealth of 
families. 
ASTEROSPONDYLI. 
Sharks with anal Jin and two dorsal Jins. 
Among the Scandinavian Sharks the families be- 
longing to this series may be distinguished as follows: 
A: First dorsal fin situated between the perpendiculars drawn 
through the pectoral and ventral fins. 
a: Eye with a nictitating membrane Fam. Carcliariidce. 
b: Eye without nictitating membrane... „ Lamnidce. 
B: First dorsal fin situated above the ventral 
fins or behind the perpendicular drawn 
through these fins „ Scylliidce. 
Fam. CARCHAKIIDjE. 
Two dorsal Jins and one anal , the first dorsal opposite to the space between the pectoral and ventral fins. Eye 
with a nictitating membrane, which is drawn up from the lower part of the orbit. Spiracles obliterated or minute. 
The hindmost or even the penultimate gill-opening situated above the base of the pectoral fin. 
According to Gunther’s definition c of this family it 
includes among its 60 — 70 species the true Hounds {Mus- 
teli) and their nearest relatives • — with small, pointed 
or flat, more or less paved jaw-teeth — as well as the 
Hammerheads ( Sphyrnce ), with their singular lateral 
production of the orbital and nasal regions. These two 
subfamilies are indeed strangers to the Scandinavian 
fauna, as far as we know at present, but approach very 
near to its limits, a species of each having been found 
on the Scotch coast, and one of these ( Mustelus vulgaris) 
a Naturl. Syst. Elasmobr., Jena 1879, Allgem. Theil, pp. 35, cett. 
6 Two, perhaps three species of this family are inhabitants of the Mediterranean and the Atlantic; and one of these species, Noti- 
danus ( Hexanclius ) griseus, is not so very rare on the English coast and has been met with so near the limits of the Scandinavian fauna as 
off the coast of Scotland. 
c Cat., vol. VIII, p. 353. 
