122 Prof. Agassiz on Fossil Fishes. 



bones concur in the formation of the parietal crests ; the external 

 occipital behind, the parietal bone in the centre, and the frontal bone 

 in the anterior portion. The lateral portions of the nape descend 

 almost perpendicularly, to rise again subsequently, and form the 

 strong temporal crests, on to which are articulated the opercula. 

 The temporal grooves which are formed by these crests, rise gra- 

 dually towards the projection of the front, but they never reach the 

 length of the parietal grooves. Lastly, below these grooves are 

 situated two smaller mastoidean grooves, comprised between the pos- 

 terior frontal and the temporal crest, which continues behind the 

 preoperculum over the operculum. The front is made up entirely 

 of the two frontals ; it forms a perfectly level surface, which is even 

 slightly depressed on the median line, instead of being raised, as in 

 many other fish. The frontals are wider behind than in front, and 

 their orbital portions descend in the form of an arc along the two 

 sides. This arc is completed in front by the anterior frontal, above 

 which the principal frontals terminate suddenly, as if truncated. 



The nasal is encased between the two principal frontals by a flat- 

 tened protuberance, the upper surface of which is a continuation of 

 the surface of the front, but subsequently it descends almost verti- 

 cally, forming a sharp-edged and very narrow crest ; between this 

 crest and the anterior frontal there is a very deep groove, which is 

 limited anteriorly by the suborbitals and the upper jaw. 



The first suborbital is of immense size, trapezoidal, with rounded 

 margins. Its anterior portion is porous, its posterior portion squa- 

 mose, and folded in plaits, radiating from above downward. 



The preoperculum is long, narrow, especially above, where it 

 forms a crest which descends vertically. The horizontal part is 

 very short, the margin (limbe), by which the corner of the " equerre" 

 is bordered, is coarsely folded in radiating plaits. The whole of the 

 orbital fossa between the preoperculum and the suborbital is coated 

 with scales resembling those of the body. 



The upper maxillaries are almost entirely hidden under the sub- 

 orbitals ; they are widened behind, and in connection anteriorly with 

 the ascending branch of the intermaxillary, which is short, curved 

 like a bow, and furnished on its lower margin with a series of strong, 

 crooked teeth, whose length diminishes from the front hindwards. 



The inferior maxillaries are short and high ; they are provided, 

 like the intermaxillaries, with crooked teeth, which, hindwards, 

 are in simple rows, while at the symphysis there are several placed 

 one behind the other. The teeth diminish hindwards in the same 

 manner as those of the intermaxillary ; the canines are not observed 

 to be more projecting than the others. I am not able to say whe- 

 ther the palate and the tongue were likewise provided with teeth, 

 but the generic position of our fish leads me to presume that they 

 were smooth. 



The opercular pieces are covered with several rows of scales per- 



