580 H. H. SWINNEHTON. 



streugtlieu the conviction that these foi-ins should he referred 

 to a separate sub-order. I propose, therefore, that these fishes, 

 hitherto placed iu the sub-orders Heinibranchii and Lopho- 

 brauchii, should be put together in one sub-order, having the 

 name Thoracostei,^ as expressive of the presence in all of a 

 more or less complete bony armature, and especially of infra- 

 clavicles. 



The two old sub-orders might still be provisionally retained 

 as divisions until such forms as SolenostomaandAulorhynchus 

 have been tlioroughly examined ; but. in viev^ of the facts 

 already put forward, the sticklebacks should certainly be 

 referred to a separate division, the Gasterosteoidei. 



One feature of great interest about the Thoracostei is tlie 

 possession of undoubted highly specialised characters side by 

 side with primitive ones, which indicate that they branched 

 off from lowly physoclistous, or even physostomous fishes. 

 We may now briefly inquire into their relationships to other 

 fishes. 



To the best of my knowledge, the nearest approach to this 

 order among living fishes is made by the Scomberesocidae. 

 Indeed, so close is this approach that on a cousideration of 

 the head skeleton alone one would be almost obliged to place 

 Belone in the same sub-order with Gasterosteus. Give its 

 cranium an arched instead of a flattened roof, replace its ali- 

 sphenoid by overlapping frontal and par:is{)lienoid processes, 

 shorten thepremaxilheand mandible to a normal length, elon- 

 gate the symplectic still further, and it would be extremely 

 difficult to find any feature of importance in which the two 

 crania differed, for iu the Belone all the roofing bones are 

 sculptured; in spite of its lowly affinities, its opisthotic is 

 absent ; the ethmoid, though more cartilaginous, is of the same 

 type ; the branchial apparatus is an exact replica of that in 

 Gasterosteus in the number and nature of the basibranchials, 



1 Since I lie above was wriUen, Smith Woodward lias })ublislied liis mucli- 

 iieeded fourth volume of tlie ' Catalogue of Fossil Fishes in the Biiiibh 

 Museum.' In this he has united the two old siih-ordeis under the one name 

 liemibranchii. 



