62 2 TELEOSTEI chap. 



should be removed from this physostomous sub-order. The 

 two families have many characters iii 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 Lyonieri (Halosauridae) and Heteromi (jSTotacan- 

 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. S. 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 

 NotacantJius, 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 Fierasfer 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 wbich 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." 

 ^ Fauna u. Flora d. Golf. v. Ncaii. ii. 1880. 



