1128 



SCANDINAVIAN FISHES. 



(12 — l-i) floes not extiHid lieyoiul tlic l>riiiiclii;il a))er- 

 tures, sometimes not even to tliem, and lliut tlie nian- 

 (lilinlar l)raiich is continuous witii tins canal. 



In Scandinavian waters Sharks are less common 

 and conse(|iiently less kno\vn and feared tlian in more 

 temperate or tropical seas. Ahout one liundred and 

 lit'ty species are recognised, but of these oidy eleven 

 can be claimed for the Scandinavian fauna. 



In the sketch given by Hasse" of the evolution of 

 the Elasinobranchs one group, the Pnlf<viii(ifi(hn/i, in the 

 present age most nearly re})resented by the NntidankJa'' , 

 a family foreign to Scandinavia, rank as the primordial 

 type botii of the Sliarks and Rays. Externally this fa- 

 mily is chai-acterized b)' the possession of only one 

 dorsal tin, l)ut of six or seven gill-openings. Tlie proofs 

 of its jjrimitive nature must be sought, however, in the 

 structure' of the spinal column, with its undifferentiated 

 vertebra". From the Palceonotidani, according to Hasse, 

 three diffei-eiit evolutional series may be traced, with a 

 calcified double-cone, more or less distinct and of varying 

 development, in the centra of tiie vertebra-. Its deve- 

 lopment is most imperfect in the so-called Cijdospon- 



dijVi, wiiei'e it appears mereh- as a ring of calcitication. 

 Externallv all these Sharks (tlie fainih" Spiiiacidce), with 

 their typical form of bod\-, may Ix? recognised In- 

 their want of anal tin. In tlje (jther two evolutional 

 series tlie double-ccme (composed of two more or less 

 deeply hollowed cones, contluent at the vertices) is 

 generally developed to such a degree tiiat the bodies 

 of tlie vertebra? are fully amphicadous; but in one of 

 tliem —the so-called Tectospondi/Ii — it consists of 

 smooth, concentric layers of calcitication, in the other 

 — the so-called Astemspondi/li — 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-tishes (Bhinidce) and the Saw-Sharks {PriMiophii- 

 rid(e), 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 tin and two dorsal fins — are Afiterospondyli, 

 and in this series the Plagiostomous type has attained 

 its richest dcn'elopment, with the greatest wealth of 

 families. 



ASTEROSPONDYLI. 



SJiark.'^ ivitli aind tin mid tint dorsrd fins. 



Among the Scandinavian Sharks the families be- 

 longing to this series ma_v be distinguished as follows: 



A: First dorsal fin situated between the pcrpemlicnlars drawn 

 through the pectoral and ventral fins. 



a: Eye with a nictitating membrane Fam. Carcliariida. 



b: Eye without nictitating membrane., ,, Lainnidn: 

 B: First dorsal fin situated above the ventral 

 fins or behind the perpendicular drawn 

 through these fins , Scylliidce. 



Fam. carchariidj:. 



Two dorsal Jins niid one amd, the first dorsal opposite to the space hetween the pectoral and central fins. Ei/c 



n-ifh (I nictitathuj membrane, which is drawn up from the lower part of the orbit. Spiracles obliterated or minide. 



The hindmost or even the penultimate gill-openinfj situated above the base of the pectoral fin. 



According to GC'ntheh's definition' 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 



l)roduction of the orl)ital 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 sjiecies of each having been found 

 (m the Scotch coast, and one of these {]]fHstelas nilyaris) 



" Natiirl. S'jst. Elasmobi:, .Jeuii 18711, ^Ulgeni. Theil, pp. U.'j, cett. 



'■ Two, perhaps three species of lliis family are inhabitants of the Mediterranean and the Atlnntio; and one of these species, Noti- 

 ,l'iiiti.< {lle.tnndnis) griseus, is not so very rare on the Englisli coast and has been met with so near the limits of the Scandinavian fauna as 

 off the coast of Scotland. 



•■ Vat... vol. VIII, p. ;i53. 



