— 157 — 



show, better even tlian those of the other fishes of the group, that this external portioii of these 

 primarv bones is formed by osseous accretions that are apparently developed in exactly the same 

 way as the corresponding portions of the purely dermal bones. A 13 cm specimen was treated with 

 chlorine, in an early attempt to trace the sutures between the cranial bones, and m this preparation 

 a superficial layer of bone coiild be stripped off from both the purely dermal and the primary bones, 

 leaving, in the forraer case, a thin remaining plate of bone which may perhaps represent a separate, 

 membrane component underlying a more important dermal or latero-sensory component. This 

 membrane component would then be the part that persists in those higher animals in which the 

 latero-sensory component has disappeared. 



The skull of Dactylopterus is said by Cuvier & Valenciennes ('29, vol. 4, p. 131) to be depressed 

 and widened in such a manner that it represents a subrectangular disk, the anterior edge of which 

 is curved in an obtuse angle, and its posterior angles prolonged into long points. A very large median 

 ethmoid and two prefrontals are said to form an anterior row of the bones that form the pavement- 

 hke dorsal surface of the skull. A second row is said to be formed by the large frontals, behind each 

 of which bones there is a small postfrontal. A third row is formed by the median interparietal, the 

 two parietals, and the two mastoids; and a fourth row by the two external occipitals and two 

 suprascapulars. Between the tliird and fourth rows, on either side, two oval bones are said to be 

 intercalated, these two bones together, on each side, representing the ,, rocher". 



The prefrontals of this terminology are the ectethmoids of the nomenclature employed by 

 me, the interparietal is the supraoccipital, and the mastoid is the pterotic. The term ,, rocher", as 

 used by earlier authors, is said by Starks ('Ol) to be the synonym of the opisthotic of later authors; 

 but it will be shown that the so-called ,, rocher" of Dactylopterus is the lateral extrascapular, and 

 not the opisthotic of the fish, this latter bone being whoUy absent. It will be further shown that 

 the external occipital is a mesial extrascapular, and not an epiotic; and, what is much more important, 

 it will be shown that the median ethmoid is not an ethmoid bone at all, but is a median bone formed 

 by the fusion, in the middle line, of the two nasals. 



Gill ('88) calls the median ethmoid of Cuvier and Valenciennes the prosethmoid, and says 

 that it and the anteal (vomer) are ,,entirely disconnected, leaving a capacious rostral Chamber opening 

 backwards mesially into the interorbital region". Into this rostral Chamber the well developed ascend- 

 ing pedicles of the intermaxillines (premaxillaries) are said to glide. And as Gill, in his descriptions 

 of the Loricati, says that the ascending pedicles of the intermaxillines glide ,,over the front of the 

 prosethmoid", the term prosethmoid, as used in his descriptions of Dactylopterus, is certainly intended 

 by him to designate a bone that he considered as the strict homologue of the median, primary 

 mesethmoid of current descriptions. No mention is mad,e of a rostral either by Gill or by Cuvier 

 and Valenciennes. 



The floor of the rostral chamber, in my medium-sized specimens, inclines downward and 

 forward at an angle of about 45". In the 41 cm and 35 cm specimens this floor is somewhat less steep, 

 while in the small specimens it is much steeper. In the middle line of the anterior half of the floor, 

 there is a narrow strip of cartilage formed by a median rod-like projection from the anterior end 

 of the antorbital cartilage. This rod-like process is the strict homologue of the prenasal process, 

 or beak, of my descriptions of Amia and Scomber, but it is here a relatively long and narrow rod, 

 curving downward and forward. It lies in a median groove on the dorsal surface of the vomer, and 

 extends to the anterior edge of that bone, agreeing in this with the arrangement fouud in Scomber. 



