622 TELEOSTEI CHAP. 
should be removed from this physostomous sub-order. The 
two families have many characters in common, such as the 
attachment and structure of the pectoral arch, which is devoid of 
a post-clavicle, the position of the pectoral fins high up the sides, 
the strong parapophyses inserted very low down on the centra of 
the vertebrae, the extent of the parietal bones, which meet in 
a sagittal suture and separate the frontals from the supra- 
occipital. The recent discovery of a third family, the Lipo- 
genyidae, which, in the structure of the dorsal fin, is exactly 
intermediate between the two others, has lessened the gap 
between the Lyomeri (Halosauridae) and Heteromi (Notacan- 
thidae) of Gill, which I have proposed to unite in a sub-order 
under the latter name. 
These Fishes are no doubt derived from forms in which a 
separate caudal fin existed; such a type must have been near 
the Dercetidae, as defined by A. 8. Woodward, which may 
provisionally be placed here. 
An imperfectly known Fish from the Chalk of Mount Lebanon, 
Pronotacanthus sahelalmae, appears to bear some affinity to 
Notacanthus, and has been placed in the same family; but its 
characters are not sufficiently defined to refer it without doubt 
to this division. 
There is a fifth family which may enter this sub-order: 
the Fierasferidae, the structure of which has been exquisitely 
described and figured by Emery.’ Hitherto placed with or near 
the Ophidiidae, they differ widely from them, as well as from 
all Acanthopterygians, in the conformation of the skull, the 
supraoccipital being separated from the frontals by the parietals, 
which form a long median suture. This is a feature which has 
only been observed in Fishes with abdominal ventral fins, and 
although the total absence of those fins in Fverasfer deprive 
us of an important criterion in deciding on its affinities, I am 
inclined to regard this family as derived from an “abdominal ” 
type. The conformation of the pectoral arch has much in 
common with that of the Halosaurs, and, notwithstanding the 
interpretation that has been given to the bones at the back of 
bladder passes anteriorly into a tapering band of tissue which ends in a thread- 
like ligament attached to the stomach near its posterior end and in the mid-dorsal 
line—not to the oesophagus ; no trace of an open communication could be found.” 
1 Fauna u. Flora d. Golf. v. Neap. ii. 1880. 
