GEN. ACANTHIAS. PICKED DOG-FISH. 313 



confounded with any otlior, owing to the extra- 

 ordinary length and form of the tail, which is as 

 long as the whole body. There is only one species, 



(Sp. 227.) A milpes^ Fox-shark, or Thresher, a 

 fish of considerable size, frequently measuring thir 

 teen feet in length, including the tail. In a speci- 

 men of these dimensions the latter usually measures 

 upwards of six feet. The imder lobe is very small 

 and the upper is slightly curved upwards, and re- 

 sembles the blade of a scythe. It is the form of 

 this appendage which has caused this shark to be 

 named the Sea-fox, and it obtains the appellation of 

 Thresher from its habit of attacking other fishes 

 and the cetacea, striking them violently with its tail 

 so that voyagers often hear the sound of the strokes 

 at a considerable distance. It has been observed to 

 approach a herd of dolphins sporting in security on 

 the surface, and by one splash of this formidable 

 weapon scatter them in alarm in every direction. It 

 is by no means plentiful in our seas, but has been 

 observed in many different localities. Last season 

 a fine specimen was exhibited at a meeting of the 

 "Wernerian Society, which was caught at Largo 

 Bay, in August 1842. 



Gen. CXIII. AcANTHiAS. — Has the general as- 

 pect of Scyllium and Mustelus : the presence of a 

 single strong spine, in front of each of the two dorsal 

 fins, affords the means of distinguishing it at once 

 from all the other sharks. 



(Sp. 228.) A. vulgaris. Picked Dog-fish. The 

 most common of all tlie sharks, and found in every 



