232 FISHES. 



is occasioned by the air rushing out of their stomach. Each of their nos- 

 trils is furnished with a double fleshy tentaculurn. 



DiodoNj Lin. 



The Diodons are so called because the jaws are undivided and formed of 

 one piece above and another below. Behind the trenchant edge of each of 

 these pieces is a round portion transversely furrowed, which constitutes a 

 powerful instrument of mastication*. The skin is everywhere so armed 

 with stout pointed spines, that, when inflated, they resemble the burr of a 

 chestnut tree. A number of species inhabit the seas of hot climates. 



Some of them have long spines supported by two lateral roots. 



The most common of this group, Diod. atinga, Bl. 125, and bet- 

 ter, Seb. Ill, xxxiii, 1, 2, is more than a foot in diameterf. 



Others have short spines, proceeding from three diverging roots J. 



Some again have spines as slender as pins or hairs §. 



Tetraodon, Lin. 



The Telraodons have the jaws divided in the middle by a suture, so as 

 to present the appearance of four teeth, two above and two below; spines 

 on the skin small and low. Several species are said to be poisonous. 



T. Uneatus, L. ; Fahaca of the Arabs ; Fiasco psaro of the 



Greeks; T. physa, Geoff., Poiss. d'Egypt. I, 1; Rondel. 419. 



Back and flank longitudinally striped with brown and whitish. 



From the Nile, which, during its inundations, casts thousands of 



them on shore, where they serve' as play things for the children. 



Some of them have a laterally compressed body, and a somewhat 



trenchant back; their power of inflation must be less than the others. 



One of them is electrical II. 



* Fossil jaws of this description are not uncommon. 



t The Diod. histrix, Bl. 126, is the same species uninflated. To avoid all equivo- 

 cation, I call it Diodon punclatus ; — Add, Diod. spinosissimus, Cuv., Mem. Mus. IV, 

 p. 134, Seb. Ill, xxiv, 10;— Diod. triedricus, Cuv., Mem. Mus. IV, p. 133, Seb. II, 

 xxiii, 4; — D. nictemerus, Cuv., loc. cit. IV, vii, 5; — D. novem-maculatus, Id., lb. VI, 

 .">; — D. scx-maeulatus, Id., lb. Vll, 1; — D. multi-maculutus, Id., lb. 4. 



X Diod. tigrinus, Cuv., Mem. Mus. IV, vi, 1, or orbiculatits, Bl. 127, Seb. Ill, xxiii, 

 3; — D. rivulattts, Cuv., lb. 2, or maculato-strialus, Mitch. VI, 3, probably the Orbe, 

 Lacep. I, xxiv, 3; — D. jaculiferus, Cuv., loc. cit. VII, 3; — D. antennatus, Id., lb. 2. 



§ Diod. piloms, Mitchil. 1, 471. 



|| The head and tail of the fishes of this genus are generally smooth, but the rest 

 of their body is rendered more or less rough, by the very small spines which arise from 

 the skin. The various combinations of the smooth and rough parts, and the different 

 configurations resulting from the more or less oblique form of their head, have al- 

 lowed me to arrange them in the following manner: — 



I. Species with a short head, possessing the faculty of inflating themselves so as 

 to attain a globular form. 



1st. The entire body rough. 



A. Immaculate; — Tetr.immaculatus, Lacep. I, xxiv, 1, Russel, I, 26. 



B. With black spots;— Tetr. mouchete, Lacep. I, xxv, i, or T. Commersonii, Schn., 

 Iluss. I, 28; — Tetr. ftuviatilis, Buchan. XXX, 1; — Tetr. geometricus, Bl. Schn., 

 Catesb. II, xxviii. 



C. With black bands;— Tetr. fahaca, or T. physa, Geoff., Poiss. d'Eg. I, 1 ;— T. 

 Uneatus, Bl. 141, tu which the Tetr. psittatus, Bl., Schn. 'Jo, is at least closely allied. 



