CKAIVIAL OSTEOLOGY OF THE OSTEOGLOSStD^. 265 



completely roofed ; its aperture is triangular in the small specimen, 

 but rounded in the large one; it is bounded by the epiotic, 

 opisthotic, and squamosal. Its anterior blind end is limited by 

 the supraoccipital, parietal, and squamosal bones. 



The occipital half-centrum presents a shallow concavity behind, 

 and is readily separable from the basioccipital and exoccipital 

 bones. The vertebral centrum behind this may also be regarded as 

 a constituent of the cranium, since its lower portion is continu.ed 

 forward into two parallel processes, right and left, which are 

 rigidly united by long jagged sutures with the back of the para- 

 sphenoid. The parasphenoid bears a long patch of crowded 

 small teeth, and from its lateral edges there project, as in 

 Osteoglossum and Seterotis, a pair of strong processes which 

 enter into definite articulation with the entopterygoids. Each 

 lateral process of the parasphenoid projects sliglitly forward, and 

 is covered by synovial cartilage on its anterior edge. The vomer 

 is a flat bone, bearing crowded small teeth similar to those of the 

 parasphenoid. The mesethmoid is almost entirely cartilaginous ; 

 there is a small median endosteal ossification lying between the 

 nasals above and the vomer below, but it does not present itself 

 on the surface of the skull. 



The orbitosphenoid is a paired bone of small vertical extent, 

 in contact with the f rentals above and the parasphenoid below. 

 The orbitosphenoids reach the prefrontals in the large specimen, 

 but not in the smaller : they are apparently separated from the 

 alisphenoids behind. Unfortunately the alisphenoids are missing 

 from both specimens, as also is the basisphenoid bone. 



Temjjoral and Preopercular Series (fig. 15). — The post-temporal 

 consists of a curved flake of bone continued forward into a point 

 which rests over the epiotic pominence. The sensory canal tra- 

 verses its lateral edge horizontally ; the deep or opisthotic limb 

 is well developed and is almost as long as the epiotic limb. The 

 bone is not sculptured. In the larger specimen, owing to the 

 forward spreading of the bone diminishing the space between 

 the epiotic and opisthotic limbs, these limbs appear shorter than 

 iu the smaller specimen. 



The horizontal limb of the preopercular is about as long as 

 the upright limb, and makes an angle of 90 degrees with it. The 

 strong development of the horizontal limb of the preopercular, 

 taken in conjunction with the slope of the hyomandibular, points 

 either to a reduction in the length of the gape, or to an increase 



