III. COTTOIDS OF NOKTH AMERICA. 15 



vided with card-like teeth. The vertical portion is composed of a spine and a 

 flattened process situated behind the spine, but in close contiguity with it, and 

 reaching only to half the height of the latter. The maxillary (21) which con- 

 stitutes with the premaxillary the upper jaw, is articulated anteriorly with the 

 vertical branch of the premaxillary, and a little covered by the suborbitals. Its 

 posterior extremity is kept movable on the membrane, which forms the angle of 

 the mouth. Its form is elongated, slender, a little curved, subcylindrical, flattened 

 behind, and provided in front with an articulating trifid head. 



The vault of the palate is formed by three bones, closely soldered together, 

 constituting an arcade, which rests behind on the hypotympanic and pretympanic, 

 abutting in front against the vomer and premaxillary. The first of these bones is 

 the palatine (20), irregular in shape, and provided with several flat, wing-like 

 expansions, on which no teeth can be seen. The entopterygoid (23), and pterygoid 

 (24), come next to the palatine; they are both of nearly the same length, and 

 so intimately connected that we did not venture to separate them for fear that 

 we should break the only specimen which was at our disposal. The pterygoid 

 is uniformly elongated and flattened; the entopterygoid is flattened and elongated 

 also, but terminated posteriorly in an expansion, crescent shaped behind, resem- 

 bling somewhat a forked caudal fin. 



The dentary (32), is not quite as much curved as exhibited in the figure. Teeth 

 exist on the whole width and length of the upper branch, which extends a little 

 more backwards than the lower one. 



The articular (29), has still adherent to it the angular (30), at its lower and 

 inferior corner, and the splenial (31) inwardly and above, which for the same 

 reason as mentioned in the case of the pterygoid and entopterygoid, we did not 

 attempt to separate. The angular and splenial are very small bones, insignificant 

 in their shape, which could only have been drawn of natural size with great diffi- 

 culty. Our object is to signalize their presence and their homology. The articular 

 itself is a stout and well developed bone, and so characteristic in all osseous fishes 

 that it could hardly be mistaken. The hypotympanic (28), irregularly triangular 

 in shape, is provided at its summit with a rounded head which articulates on the 

 articular and splenial. The body of that bone is a flat disk protected on each side 

 by a spine which extends a little beyond the central disk. Above the hypotym- 

 panic, and encroaching into the forked extremity of the entopterygoid, is the pre- 

 tympanic (27), a very thin leafy bone, so delicate that in detaching it from its 

 neighbors it is constantly torn along the edges. As represented in the figure, 

 the outline above has lost its actual shape. The mesotympanic (26), is likewise 

 almost a mere membrane, or a thin cartilage, in the middle of which two points of 

 ossification are distinctly seen. The mesotympanic forms the continuation of the 

 lower extremity of the epi tympanic. The epitympanic (25), itself, articulates above 

 with the mastoid. It is somewhat covered by the upper part of the preopercular. 

 The epi-, meso-, pre-, and hypotympanics are all intimately connected, and form the 

 back roof of the mouth, limited behind by the concavity of the preopercular. The 

 palatine arcade extends from its anterior edge to the vomer and premaxillary, thus 

 continuing the roof to the anterior part of the mouth. The upper angle of the 



