556 H. H. SWINNERTON. 



connection may have been lost through the coincidence of 

 these two features ; but a comparison of figs. 43 — 53 (each of 

 which has been drawn so that the whole skull would be the 

 same length as that indicated in fig. 43^ from the tip of the 

 ethmoid to the arrow marked *) shows that this is not the case, 

 for both Belone (fig. 49) and Gasterosteus (fig. 51) have a 

 short ethmoid as compared with that of the pike and 

 Scomber ; and the former at the same time possesses a long 

 mandible. If a long ethmoid were a condition necessary to 

 the absence of post-palatine articulation, then it should be 

 absent in the pike. Again, if a long gape and short ethmoid 

 were the essential accompaniments of a double attachment, 

 the Belone should have this. But as the pike possesses a 

 well-formed post-palatine attachment, and the Belone does 

 not, it becomes clear that the two types are wholly indepen- 

 dent of either length of ethmoid or size of gape. 



When, in connection with these facts, we consider that both 

 the single and double types are quite distinct throughout deve- 

 lopment, that notwithstanding all the changes of form which 

 the head undergoes among Acanthopterygii, from the short- 

 snouted Bovicthys to the long-snouted Scomber, from the 

 deepened Drepane to the flattened Platycephalus, the double 

 articulation is retained, we cannot refrain from concluding that 

 the distinction we make between the two types is not a super- 

 ficial one, and that the single articulation is due, not to 

 the existence of a long-snouted Lophobranch or Plectognath, 

 but that these owe their origin to the existence of this type. 

 Whether this conclusion is right or wrong, future work alone 

 will decide ; meanwhile, the fact remains that two such types 

 exist, and consequently the necessity arises in descriptive 

 work for distinguishing between them concisely. Accord- 

 ingly, all forms possessing both pre- and post-palatine 

 articulations, irrespective of the possession or non-possession 

 of a rostrum, mny be described as Disartete; and all 

 possessed only of the pre-palatine articulation, and of an 

 ethmoid whose pre-ethmoid cornua are situated on each side 

 of its anterior extremity, may be described as Acrartete. 



