BONES FORMING OPERCULAR SERIES OF FISHES 6/ 



borders the lower margin of the interoperculum ; all soem to arise 

 from the outer face of the hyoid arch, but the anterior two are 

 somewhat separated from the upper posterior four, which, unlike 

 those of Regalecus, are largely covered by the expanded preoper- 

 culum. In Trachypterus rex-salmonorum the branchiostegals are 

 concealed by the interoperculum as well; and the low-er two rays, 

 considerably separated from the upper four, are attached to the 

 outer side of a ligament which extends as a chord across the 

 concave antero ventral margin of the hyoid arch. 



The Ammodytoidea are another group which has been placed 

 by some ichthyologists among the higher teleosts, by others 

 among the lower. The branchiostegals in .\mmodytes personatus 

 resemble those of the Acanthopteri in most of their characters: 

 they are six in number, and are folded up behind the opercula; 

 the upper four arise from both the cerato- and epihyal behind a 

 prominent angle of the arch. The lower two rays, however, arise 

 from the outer surface of the arch, and are closely approximated 

 to the upper four. 



The Microcyprini (Poeciliidae and Amblyopsidae) were long 

 confused with the Haplomi, but have recently been shown to have 

 a more advanced organization. The structure of the branchi- 

 ostegal rays in the two groups confirms this \dew: those of the 

 Haplomi are quite like those of the Isospondyli, whereas those of 

 the Microcjrprini are similar to those of the Acanthopteri. In 

 the Poeciliidae there are six, or fewer, branchiostegals, which are 

 folded up behind the operculum and above its lower margin. The 

 upper four saber-shaped rays are attached to the outer surface 

 of both the ceratohyal and epihyal, postero-superior to the 

 prominent angle of the hyoid arch ; the lower rays arise from the 

 inner face of the ceratohyal. In examples of the Ophicephalidae 

 and Anabantidae at hand (representing the order Labyrinthici) , 

 there are four plus two branchiostegal rays, arranged as in the 

 Microcyprini and Acanthopteri. 



Many of the aberrant fishes referred to the order Hemibranchii 

 have the branchiostegals reduced in number, but in Fistularia 

 there are four plus one rays, arranged as in typical Acanthopteri. 

 "Most Lophobranchs have two branchiostegals, but Nerophis has 



