304 CARTILAGINEI. — SQUALID^. 



some or otlier of which are scattered over all 

 seas. Fifteen are enumerated among British 

 Fishes, either as habitual residents in our waters, 

 or as accidental stragglers. Considerable diffi- 

 culty is felt by naturalists in the attempt to 

 subdivide the family into natural groups ; not 

 from the number of the species so much as from 

 the diversities of form and structure that exist 

 among them. The following is the arrangement 

 proposed by Mr. Swainson. 



HAMMER SHARK AND SAW FISH. 



1. Zygcenina. The Hammer-heads. These have 



