170 Mr. G. A. Boulenger on the Suborders and 



Suborder VI. Heteromi. 



Air-bladder without open duct. Opercle well developed ; 

 parietal bones separating the frontals from the supraoccipital. 

 Pectoral arch suspended from the supraoccipital or the epiotic, 

 the post-temporal small and simple or replaced by a ligament ; 

 no mesocoracoid. Ventral fins abdominal, if present. 



The Halosauridse and Notacanthidaj are deep-sea fishes of 

 obscure affinities. In the abdominal position of the many- 

 rayed ventral fins and in the absence of the mesocoracoid arch 

 they agree with the Haplomi ; but if, as the investigations of 

 Gunther lead us to believe *, there is really no open commu- 

 nication between the air-bladder and the digestive tract, they 

 should be removed from this physostomous suborder. The 

 two families have many characters in common, such as the 

 attachment and structure of the pectoral arch, which is devoid 

 of a postclavicle, the position of the pectoral tins high up the 

 sides, the strong parapophysis inserted very low 7 down on the 

 centre of the vertebras, the extent of the parietal bones, which 

 meet in a sagittal suture and separate the frontals from the 

 supraoccipital. The recent discovery of a third family, the 

 Lipogenyida?, which in the structure of the dorsal fin is so 

 exactly intermediate between the two others, has lessened the 

 gap between the Lyomeri (Halosaurida?.) and Heteromi 

 (Notacanthida3) of Gill, which I propose to unite in a suborder 

 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 Dercetidaa, as defined by A. S. 

 Woodward, which may provisionally be placed here. 



There is a fifth family which may be placed in this sub- 

 order, the Fierasferidas, 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 other Acanthopterygians, in the 

 conformation of the skull, the supraoccipital being separated 



* Yaillant was inclined to lake a different view, but with considerable 

 diffidence, owing to his inability actually to trace an open duct. 1 believe 

 Gunther to be right on this point, as well as in his account of the suspen- 

 sion of the pectoral arch in Notacanthus, which I have been able to verify. 

 Besides, Mr. W. S. Rowntree, who has great experience in these matters, 

 has kindly examined at my request a well-preserved example of Halo- 

 sauropsis macrochir, and informs me that " the air-bladder passes ante- 

 riorly 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." 



