PLECTOGNATHI 



723 



Salimochirurgus. The latter, remarkable for its long, tube-like 

 snout, is the only deep-sea form of this Sub-order ; it was recently 

 discovered in the Gulf of Manaar, at a depth of 143 fathoms. 

 Fossil genera are Acanthopleurics, Oligocene, and Spinacanthus, 

 Eocene. 



Fam. 2. Triodontidae. — Praemaxillaries not protractile, 

 firmly united to the maxillaries ; teeth coalescent into a beak, the 

 upper jaw divided by a median suture, the lower simple. Prae- 

 caudal vertebrae with or without, parapophyses ; epipleurals 

 present. No spinous dorsal fin. No ventral fins. Abdomen 

 with a dilatable sac, kept expanded by the very long movable 

 pelvis. Body covered with small, spiny, subimbricate, bony 

 laminae. Yertebrae 20. 



A single species, the curious Trioclon lursarhis of the Indian 

 Ocean and Archipelago. 



Fam. 3. Balistidae. — Praemaxillaries not protractile, firmly 

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

 ably articulated with ectopterygoid, or entirely free from it. 



Fig. iS7. —Monacanthus, sp., ^vith enlarged views of dorsal scales (6) and 

 ventral spine (c). 



Gills 4. Praecaudal vertebrae with well-developed parapophyses, 

 to which epipleurals are attached. Spinous dorsal fin with 1 to 

 3 spines. A^entral fins, if present, represented by a single short 



