230 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxiv. 
a. Pelvis very long, supporting the fan-shaped ventral area; upper jaw divided by a 
median suture; lower jaw undivided; skin covered with rough plates; nostrils 
as usual among fishes Triopontid.k I. 
aa. Pelvis and ril^s obsolete. 
Ik Caudal region normally developed, with a caudal peduncle. 
c. Upper and lower jaw each divided by a median suture; maxillaries and 
dentaries each curved outward behind the premaxillaries; ethmoid more or 
less projecting in front of frontals; postfrontals extending outward at least 
as far as frontals. 
d. Vertebrae comparatively few, 15 to 21 in number; dorsal and anal short, of 
7 to 15 rays. 
e. Back broadly rounded; frontal bones articulated with the supraoccipital, 
postfrontals confined to the sides; ethmoid short, narrow, little promi- 
nent to view above; vertebrte few; head broad; nostrils various. 
Tetkaouontid.f. II. 
ee. Back more or less sharply ridged; frontal bones separated from the 
supraoccipital by the postfrontals, which meet in the middle; ethmoid 
prominent above, enlarged and narrowed forward; snout pointed; 
dorsal and anal very short; nostrils obsolete or very small. 
TROPIDICHTHYIDyE III. 
cc. Upper and lower jaw each undivided, the premaxillary and dentary bones 
coossified into sutureless arches; maxillaries extended laterally behind; 
body covered with stout, rooted spines DioDONTiniE IV. 
hh. Caudal region of body aborted, the body truncated behind the dorsal and 
anal; jaws each without median suture Molid.e V. 
Family I. TRIODONTID^. 
Body covered with small, bony, scale-like, partly imbricated laminse. 
Abdomen dilatable into a very large compressed pendant sac, kept 
expanded by a very long pelvic bone; lower par-t of sac merely a flap 
of skin, into which the air does not penetrate. Skeleton ossified, the 
ribs well developed. Dorsal and anal short. Tail long, ending in a 
many-rayed forked fin. Upper jaw divided by a median suture; lower 
entire. Nostrils normal, with two openings on each side. 
A single known species, representing a transition from the ordinary 
fishes to the Gymnodont type. 
1. TRIODON Reinwardt. 
Triodon Reinwardt, Cuvier, Rcgne Anim., 3d ed., 1829, p. 588 {hursnrius) . 
(Characters of the genus indicated above.) 
[rpsh, three; odoi>g^ tooth.) 
I. TRIODON BURSARIUS Reinwardt. 
Triodon bursarius Reinwardt, Cuvier, Regne Animal, 2d ed., 1829, p. 588, 
Sumatra. — Bleeker, Atlas Gymnodontes, 1867, j). 84, pi. x, fig, 1, Amboyna, 
Harouka, Banda. — Gunther, Cat. Fish., VIII, 1870, p. 270, Mauritius, India. 
Triodon macropteruf! Lesson, Voy. Coquille, 1830, p. 103, pi. iv, Mauritius. 
Head, 3f ; depth, with sac, 3f; depth, without sac, 3i; dorsal rays 10; 
anal rays 0. Eye large, 4 in head; mouth rather large, its cleft as 
long as eve. Color brown, with a large irregular ocellated black spot 
