LEATHER JACKETS OR FILET I SUES. 221 



get into the Crayfish-pots and eat the bait. Several of the 

 species attain to a large or fairly-large size, and are of some 

 economic importance. They may all be recognised at once 

 as Leatherjackets by even the most casual observer, on 

 account of the rough leathery skin and the sharp, often high, 

 serrated and barbed spine behind the head on the back. 

 In size, our Leatherjackets range from the wee little green 

 fellow of little more than an inch or two (Alonacanthus 

 trosstilus) up to the common large yellow one sometimes 

 known as "Chinaman" which attains to a length of upwards 

 of two feet (Monacanthus ayraudi). The barbed- 

 spine (just mentioned), at the back of the head, is really 

 the remnant of the first dorsal fin which in fishes of a 

 closely-allied genus, Balistes, still exists. It is from the 

 barbed and serrated nature of this spine, that they have 

 received the name of File-Fishes. The tough skin covered 

 over with the exceedingly rough and small scales is respon- 

 sible for the other name of "Leatherjackets," by which they 

 are most familiar to us. In these fishes both jaws are 

 armed with eight strong, incisor-like teeth, and with these 

 they are able to crush up very hard substances, such as the. 

 shells of Mollusks and Crabs, etc. Some of them are at 

 times very destructive to young edible Ovsters. Their 

 rough scutes or scales are so small as to give to the skin 

 quite a velvety appearance. Some of these scales are mush- 

 room-shaped and others are spinous. They all make most 

 interesting objects for the microscope. The term "scales"' 

 is here really not quite correct as they are more properly 

 described as "dermal papillae." Some of the species possess 

 a peculiar armature on each side of the tail, that of the 

 male being usually different to what is found on the female. 

 This armature may consist either of simple spines arranged 

 in rows, or of the development of the minute spines of some 

 of the scales on each side of the tail, into long, stiff bristles ; 

 so that a patch is formed, which looks very much like a 

 tooth-brush. Both of these different forms of armature are 

 to be found in well-known Australian species. 



As it will be quite impossible within the scope of such 

 a general little work as this, to even casually mention even 



