814 KEPORT OF COMMISSIONER OF FISH AND FISHERIES. [68"! 



In Megalops the vomer is the most anterior bone of the cranium. 

 Viewed from above, it presents a median crest with sloping sides, and 

 is overlapped by a triangular process of the ethmoid. Below it is a 

 broad semicircular plate, with a sharp spine directed backwards, which 

 is mortised into the parasphenoid. Anteriorly this plate supports a 

 raised elliptical disk, armed over its entire surface with exceedingly 

 minute teeth (Fig. 34, Vo.). The ethmoid throws out on either side a 

 curved and flattened process, directed outwards, downwards, and back- 

 wards ; against the extremity of each rests an irregular prefrontal (Fig. 

 34, Prf. Eth.). This region is completed by the anterior extremities ol 

 the frontal and parasphenoid as far as its bony walls are concerned^ 

 while its remaining parts are fashioned in cartilage. The rostrum of 

 the parasphenoid makes an angle of 45° with the plane of its body. 

 Its anterior extremity is dilated from side t® side, and articulates with 

 the vomer, as already described. The under surface of the rostrum is 

 longitudinally concave, deepest near its middle third. Its upper sur- 

 face is composed of two sides, each ■ directed upwards and outwards ; 

 thej' meet for the entire length in the median line. The lower part, 

 or body, of the parasphenoid is scooped out above to assist in the for- 

 mation of the eye-muscle canal ; its outer margins articulating with the 

 prootics (Fig. 34, Fro.). Posteriorly the parasphenoid is sharply forked, 

 but is not carried backwards quite as far as the basioccipital goes. 



The frontal s {Fr,) are separated bones, divided by a median, and in 

 the specimen rather an open, suture. Behind they overlap the squa- 

 mosals on either side, while in turn they are beneath the hinder margin 

 of the ethmoid in front. Their posterior margins are scalloped and the 

 superficies of the bones above strongly sculi)tured. 'EAt\iQV postfrontal 

 develops a prominent lateral process j the extensive base supporting it 

 so expands as to articulate with the squamosal and frontal above the 

 alisphenoid internally and the prootic below. It also assists the squa- 

 mosal in forming the anterior end of the hyomandibular facet (Fig. 34, 

 Ptf.). A median tubular foramen passes longitudinally through the 

 orbitosphenoid, below which it sends forward a peculiar little j)rocess 

 as shown in the figure. This is carried backwards as a bony division, 

 separating the alisphenoid, and forming the apex of the margin of the 

 optic foramen. The body of the orbitosphenoid articulates with a car- 

 tilaginous i3late anteriorly, while its sides, which are tipped upwards, 

 inclose a space which we will devote our attention to further on. The 

 alisphenoids are large circular bones, separated from each other by the 

 orbitosphenoid in the median line. They bound the optic foramen lat- 

 erally and form the posterior wall for the orbits. There seems to be 

 every indication that in life they are separated above from the frontals 

 by cartilage, though they articulate by suture with the postfrontals 

 and prootics (Fig. 34, As.). 



The squamosal is a very large and i)rominent bone in the cranium of 

 this fish. Above, it forms a considerable share of the vault of the skull, 



