294 MR. C. TATE REGAN OX [NoV, 4, 



ethmoid, in opposition to the Tetroclontidse, with short or narrow 

 ethmoid, not prominent. I find that in Tetrodon lagocephalus, 

 scleratus, Irevigatus, &c. the ethmoid is long, by no means narrow, 

 and at least as prominent as in any species of the so-called 

 Canthigasteridfe. The Chonerhinidae are also separated on account 

 of the increased number of vertebrte and dorsal and anal rays, but 

 as in the Tetrodontidfe the vertebrae vary from 17 to 22 in number, 

 and the dorsal rays from 6 to 19, it is scarcely logical to separate 

 from them Chonerhinus, with 24 vertebrae and 25-26 dorsal rays, 

 nor Xenoptertis with 29 vertebrae and 32-38 dorsal rays, on that 

 account alone. 



The question as to how many genera it is convenient or useful 

 to recognize in this family is a very vexed one. Perhaps, on 

 account of the many strange and abnormal featui-es which unite 

 the Tetrodontidae and distinguish them from more typical fishes, 

 one is rather apt to overlook the diiferences which exist among 

 them ; nevertheless, it is very evident that many of the so-called 

 genera are incapable of definition and cannot be maintained. 



The genera Ephippion, Tropidichthys, Chonerhinus, and Xeno- 

 pterus can be easily defined ; but I am inclined to unite the 

 remaining species in a single genus Tetrodon, as the differences 

 in the structure of the skull and of the nasal organ show so many 

 gradations that they can hardly be used for generic diagnoses. 



In Tetrodon psittaciis Bl. Schn. I find that the frontals extend 

 to the orbital margins, therefore Colomesus Gill, if a valid genus, 

 has not been correctly diagnosed. 



Genera. 



1. Tetrodon Linn. — Body oblong or elongate, broad or some- 

 what compressed, prickly or smooth. D. 6-19. A. 6-17. 

 Vertebrae 17-22. Praefrontals, frontals, and post-f rentals with 

 la,teral expansions which form the orbital roof. Nostrils either 

 separate or confluent. 



2. Ephippion Bibr. — Differs in having the body armed with 

 bony plates. Nostrils confluent. Skeleton unknown. 



3. Tropidichthys Bleeker. — Body compressed. D. 8-10. 

 A. 8-10. Yertebrfe 18. Nostrils confluent, a single small 

 aperture on each side. Ethmoid long, nan-owed forwards. Pos- 

 terior part of frontals with paired lateral crests. 



4. Chonerhinus Bleeker. — Differs from Tetrodon in that the 

 dorsal and anal fin-rays are in increased number, as are the 

 vertebra; (D. 25-26. A. 23-25. Vertebra; 24). The pra3frontals 

 small, without lateral expansions. The nasal organs are very 

 similar to those of T. paioca, but developed into a large funnel- 

 shaped rim. 



5. Xenopterus HoUard. — Differs from Chonerhinus in having 

 more vertebne and dorsal and anal rays (Vertebrae 29. D, 32-38, 



