NO. 3 TELEOSTEAN FISHES — GOSLINE 29 



In Hiodon the nasal is a tubular, L-shaped bone hooking over and 

 around the front of the nasal capsule in such a way that the front 

 of the supraorbital lateral line canal runs downward and somewhat 

 backward. The infraorbital canal runs forward and stops in a small 

 bone (the lacrimal ?) just behind the nasal capsule. The rear of the 

 capsule is rimmed by the lateral ethmoid ; this bone does not reach the 

 surface, but just below the skin gives off a forward flange that in 

 lateral view makes the lateral ethmoid look like a circumorbital (see 

 Ridewood, 1904, pi. 25, fig. 20). There is no separate supraorbital. 



Pantodon has the suborbitals continued forward as a ring of tubular 

 ossicles well up on the anterior rim of the orbit. The anteriormost of 

 these overlies but is entirely separate from the lateral ethmoid ; that 

 it represents the antorbital of the fishes dealt with above seems some- 

 what dubious. 



In Osteoglossiim, Heterotis, and Arapaima this anteriormost bone 

 becomes progressively expanded and fuses above with the frontals. 

 In Osteoglossiim at least, it bears a canal that opens out above into 

 a subdermal space above the surface of the frontals. Notopterus has 

 a similar channel in its anteriormost circumorbital. 



At this point it may be well to summarize for the isospondylous 

 fishes. The osteoglossoids (along with the mormyroid fishes ; see 

 Derschied, 1924, pp. 142-157, figs. 21-25) must be separated off at 

 once because they have a rigidly enclosed nasal capsule without di- 

 verticula and no supraorbital bone, the place of the latter sometimes 

 being taken by a canal-bearing antorbital ( ?) that fuses with the 

 frontal above the eye. 



Second, Gonorhynchus and Phractolaemus must be removed from 

 the others, because of the very peculiar (but very different) cavities 

 connected with their nasal capsules. 



Among the remaining clupeiform fishes one or two nasal capsule 

 diverticula and an antorbital-supraorbital link are generally present. 

 At least two lines of evolution have developed from this basic pattern. 

 In Alepocephalus, which has a long snout with the nostrils far back, 

 there is a large nasal sac extending forward under the lacrimal, but 

 the supraorbital sac and the supraorbital bone are missing. In the 

 salmonoid series a rather different line of development has taken 

 place. The supraorbital sac is generally retained but the anterior end 

 of the antorbital-supraorbital link degenerates ; in Argentina, for ex- 

 ample, the antorbital seems to be completely missing. Among haplo- 

 mous fishes the antorbital is always missing; a movable supraorbital 

 is present only in Esox; and there are apparently no nasal sacs. 



