416 FISHES OF THE FIRTH OF FORTH. 



The fishermen in the Firth of Forth have frequently mis- 

 taken the present species of Shark for a full-grown example 

 of the common dog-fish, they supposing that the absence of 

 the dorsal spines is entirely owing to the age of the fish, but 

 the absence of the anal fin in the Dog-Fish, and its presence 

 in the Tope, will at all times distinguish the two species from 

 one another. The essential characters of the Tope are, 

 first dorsal fin before the ventrals; last branchial opening 

 placed immediately over the anterior extremity of the base 

 of the pectorals ; teeth denticulated only on the edge placed 

 nearest the angle on the mouth ; anal fin as well as the tem- 

 poral orifices, present ; snout depressed. 



Genus MUSTELUS. — First dorsal fin in advance of 

 the ventrals ; anal fin present ; temporal orifices present ; 

 teeth blunt, forming a closely-compacted pavement in each 

 jaw. 



MuSTELUS L/EVIS.* ThE SmOOTH HoUND. 



Description. — From a small specimen fourteen inches in length. 

 Body fusifornij rounded, greatest thickness in the region of the pec- 

 torals, tapering gradually towards the caudal extremity, where it be- 

 comes compressed ; snout and head depressed ; from the tip of the 

 snout to the third gill-opening on the neck, exactly one-sixth of the 

 entire length, and one-third as far as the middle of the space between 

 the two dorsals. Colour of the head, back, and sides, of a light 

 bluish-grey, marked with numerous small white spots, which disap- 

 pear as the fish increases in age ; belly dull pearly- white. First dor- 

 sal fin rather large, of a triangular form, the height more than equal- 

 ling the base ; placed over the posterior portion of the pectorals, and 

 half-way between the point of the snout and the middle of the second 

 dorsal fin ; the lower portion of the posterior margin terminating in a 

 point directed backwards. Second dorsal rather smaller than the 

 first dorsal, and corresponding to it in form; placed a little in advance 



* Mustelus lavis, Cuv., Yarr. Squalls mustehis, Jen., Penn. Skate- 

 toothed Shark, Ray-mouthed Day, Smooth Shark. 



