XXII HETEROMI 623 
the cranium in the latter type, the same may be said, in a 
general way, of the skull. 
As pointed out by Emery, the very anterior position of the 
vent in the Fierasferidae is directly related to the curious mode 
of life of these Fishes, and the analogous condition obtained 
in various families, such as the Gymnotidae, Nemichthyidae, 
Amblyopsidae, shows it to be a character of relatively small 
systematic importance. 
SYNOPSIS OF THE FAMILIES. 
A. Vent posterior. 
a. A distinct caudal fin ; ordinary scales small or wanting, but enlarged 
scutes along the fae 5 ; ; . 1. Dercetidae t 
b. Tail tapering to a point; scales cycloid 
No spines; dorsal fin short, anal very long . : . 2. Halosauridae. 
Fins with spines, dorsal short, anal long : . 3. Lipogenyidae. 
Dorsal fin formed of a series of eee anal long, formed partly of spines 
and partly of soft rays } 4, Notacanthidae. 
B. Vent immediately behind the, eill- co peninr ; no caudal fin; scales absent 
5, Fierasferidae. 
Fam. 1. Dercetidae.—Body much elongate; ordinary scales 
small or wanting, but two or more continuous series of enlarged 
scutes along each side; mouth large, praemaxillaries apparently 
forming the greater part of the upper border of the mouth, 
which is toothed; opercular apparatus complete. Dorsal fin 
more or less extended, without spines; anal short, caudal 
separate ; ventrals with not less than 7 or 8 rays 
Dercetis, Leptotrachelus, Leptecodon, Pelargorhynchus, and 
Stratodus, from the Upper Cretaceous of Europe, Syria, and 
North America. 
Fam, 2. Halosauridae.—Body elongate, covered with cycloid 
scales, the tail tapering to a point, without caudal fin; head 
with scales; mouth moderate, bordered by the praemaxillaries 
and the maxillaries, both toothed ; suborbitals large; praeopercle 
rudimentary. Dorsal fin short, formed of soft rays, above or 
a little behind the ventrals, which are rather far back, and 
formed of 9 or 10 rays; anal very long, without spines, extending 
to the end of the tail. Ovaries transversely laminated, the 
ova falling into the abdominal cavity. Some 10 living species 
are known, referred to three genera, inhabiting the Atlantic, 
Pacific, and Indian Oceans, at depths of 500 to 1400 fathoms. 
