724 TELEOSTEI 



rough spine at the end of the long, movable pelvis. Body covered 

 with juxtaposed movable scutes or with minute rough scales. 



About 100 species are known from the tropical and warm 

 seas, one species {Balistes ca2Jriscus) occasionally wandering as far 

 north as the south coast of England. Genera : Balistes, Monci- 

 canthus, Parcduteres, Pseudcduteres, Pseudomonacanthus, Aluteres, 

 Psilocejjhcdus. The Oligocene genuS Acanthoderma is closely 

 allied to Bcdistes. 



The " File-Fishes " or " Trigger- Fishes " {Balistes), the largest 

 species of which grow to nearly 3 feet, have a powerful dentition, 

 which enables them to break off pieces of corals, on which they 

 feed, and to bore holes in the hard shells of Mollusca in order to 

 extract the soft parts ; they are themselves well protected by a 

 mail of hard, rhomboidal scales. The herbivorous Monacanthus 

 is less favoured in this respect, the rough scales being so small as 

 to give the skin a velvety appearance. 



Psilocephcdus differs from Monacanthus in its very elongate 

 head and body, the very feeble dorsal spine, the presence of a 

 mental barbel, and its more numerous vertebrae (29 or 30 instead 

 of 18 to 21). The flesh of many of these fishes is poisonous.^ 

 The drumming sounds produced by Balistes have been described 

 by Mobius.^ 



Fam. 4. Ostraciontidae. — Praemaxillaries not protractile, 

 firmly united to the praemaxillaries ; teeth incisor-like ; palatine 

 immovable. Gills 4. Praecaudal vertebrae with very feeble para- 

 pophyses and no epipleurals. No spinous dorsal fin. Clavicles, 

 coracoids, and post-clavicles much expanded. No ventral fins. 

 Body encased in a carapace formed of large, juxtaposed, mostly 

 hexagonal bony plates. Vertebrae 14 to 16. 



The species of " Trunk-Fishes " number about 20, and are refer- 

 able to 3 genera : Aracana, Ostracion, ZactojjJirys ; all belong to 

 the tropical seas, living near the bottom in shallow water. The 

 genus Ostracion is represented by one species in the Upper 

 Eocene. 



The rigid box in which these fishes are encased entails more 

 use of the dorsal and anal fins for progression than is customary 



1 Cf, Pellegrin, Poissons Vin&iieux (Paris, 1900, 8vo), which contains a 

 very full rdsumi of what is known of the to.xic properties of the various 

 Pleotognaths. 



2 Sitzi. Akacl. Bed. 1889, p. 999. 



