PERCIFORMES 



441 



enlarged. The nostrils are often modified ; the nasal sacs may protrude 

 as a papilla, the nostrils become confluent, and finally the sac open 

 freely to the exterior (Regan [344]). The papilla then becomes a mere 



Fir.. 4',4. 

 Diodon iiuwulntus, Gthr. (After Giinther.) 



appendage in which end the olfactory nerves. The oesophagus is provided 

 with a large diverticulum, which on being filled with water inflates the 

 fish to an almost spherical shape, the defensive spines scattered over the 

 body thereby being erected (Thilo [435]). These spines, fixed in the skin 

 by three basal processes, may acquire a very large size, and are the modified 

 gcales (Figs. 454-5). 



"Flo. 455. 

 Diodon maculatus, Gthr., inflated. (After Giinther.) 



Family TETRODONTIDAE. The beaks are divided by a median suture. 

 There may be as many as twenty-nine vertebrae, and small plates are 

 rarely found in the skin. 



Tetrodon, L. ; tropical seas and African rivers ; Eocene, Europe. 

 Ephippion, Bibr. ; Tropidichthys, Blkr. ; Xenopterus, Holl. ; Chonerhinus, 

 Blkr. tropical seas. 



Family DIODONTIDAE. The ' Porcupine Fish ' have beaks without 

 suture, the vertebrae reduced to twenty-two, and the skin armed with 

 epines only. 



Diodon, L. (Figs. 454-5) ; tropical seas ; Eocene, Europe ; Miocene, 

 Java, N. America. Dicotylichthys, Kaup ; Chylomyderus, Blkr. (Fig. 453) ; 

 Trichocyclus, Gthr. tropical seas. 



