1140 



.SCANDINAVIAN FISHES. 



■A very siiiiiU flap (\;ilvuK') iit the anterior niaririn. 

 They lie so far in front of the ]ierpeiidicu]ar from tlie 

 preorbital margin that the distance between them and 

 the tip of the snout is al)out 80 — 90 % of that between 

 the mouth and the same point, wliicii latter distance 

 is rather less than or sometimes equal to the length 

 of the snout. The mouth is large, its breadth at tiie 

 corners being somewhat more than ','3 of the length of 

 the head. The cleft of the mouth is sharply curved, 

 so that the lower jaw is rather long, and the distance 

 from the corners of the mouth to the middle of the 

 anterior margin of the upper jaw is about "j^ of the 

 length of the head. Externally no dermal folds are 

 visible on tiie jaws, for the small creases that lie al)ove 

 and below each corner of the mouth are concealed by 



Fig. 330. 



Heaii of a Porbeagle (Isurtts eornubicus) 213 cui 

 seen from below. ' '. iiat. size. 



the skin of the upper jaw. The teeth (tig. 329) are 

 set ill three rows. The anterior ones are the largest, 

 measui'ing in a specimen 24 din. long somewhat more 

 tjian 12 mm. or '/j of the diameter of the e3'es. They 

 are set rather far apart, of a narro^v triangular form or 

 conical, terete on the innev, but somewhat flattened on 

 the outer side. The base of the broad root is emarginate, 

 so that the tooth apjjarently has two fangs. In old 

 specimens the root has a small conical cusp on each 

 side; but this cusp is wanting in young si)ecimens, 

 sometimes even at a length of 9 dm. In both jaws 

 we find at the extreme front a small gaji, without 

 middle tooth. The upper jaw has 14 or 1.5 (10) teeth 

 in each row on either side, the number being alike 

 both in young and old. The first two teeth are large. 



the third is rather small — :ind liehinil this lies a wide 

 gaj) (diasti'ma) — the fourth and the following ones are 

 again large, but gradually decrease in size, the hind- 

 most teeth being comjiaratively minute. In the lower 

 jaw there are 12 or 18 (14) teeth on each side. The 

 gap at the extreme front is somewhat wider than in 

 the upper ja\v. The first and second teeth are the 

 largest, the others decreasing in size behind. All the 

 teeth are slightly recurved. 



The sjiiracle of the Porbeagle is extremely small, 

 resembling a hole pierced with a coarse pin. It lies 

 exactly behind the eye, separated therefrom by a dis- 

 tance of twice the diameter thereof or somewhat more 

 in large specimens. It is consec|uently situated rather 

 f\irther back than in most of the other Sharks, and has 

 many times defied detection, being probably obliterated. 

 All live branchial apertures lie in front of the pectoral 

 fin, the lower end of the iiindiuost opening terminating 

 close below the margin of this fin. This opening is, 

 however, obliquelv set, being considerabh- aiiproximated 

 below to the jienultimate aperture. In the dermal fold 

 that covers each opening, lie three j)avallel cartilaginous 

 rays (radiating extrabranchial cartilages, sec above), 

 originating from the middle of each arcli and extend- 

 ing to the edge of the opening. 



The bodv itself is almost terete, with indistinct 

 lateral line, which is best marked in dried skitis. From 

 the temporal region, above and l)eliind the eyes, the 

 line forms a slight curve above the gills and then pro- 

 ceeds in a straight direction to the lateral carina of 

 the tail. These occupy, immediately in front of the 

 caudal fin, one-fifth of the length of the body behind 

 the head. Tiiev have an almost sharp, curved outer 

 margin, and are so large that their breadth i.s ^/g of the 

 greatest breadth of the body, and that the tail just in 

 front of the caudal grooves is, more than four times as 

 broad as deep. The caudal grooves above and below are 

 deep and clothed with finer scales than the rest ut 

 the skin. 



The first dorsal fin is rather large, its base mea- 

 suring about ' g, the length of its anterior margin ,'7 

 — Vei ^^^^ ^^s height about '/g, of the entire length of 

 the body. Its beginning lies at a distance from the 

 tip of the snout measuring about .'50 — ?>'! % of the length 

 of the body. In form it resembles an almost e(|uilateral 

 triangle, with a large rounded incision above the elon- 

 gated posterior angle. The posterior dorsal and the 

 anal fins are almost similar in form and size, and lie 



