218 DR. K. W. SHUFELDT ON [Apr. 1, 



The posterior nasal fossae are elongo-pear-shaped apertures with 

 the bulbous ends directed backwards, while either palatine foramen 

 is of an oval outline and of no great size. The inferior temporal 

 fossa is capacious, and a firm thin plate of cartilage standing verti- 

 cally in the median plane divides the orbital cavities internally. 

 This is the uderorbital neptum. 



Of fair extent, tlie basis cranii is nearly a horizontal surface, 

 showing but a very shght general concavity over it. This is at 

 variance witii such a form as Iguana tuberculata, where the area 

 to which we refer is considerably concaved. In a previous paragraph 

 we have already sufficiently referred to the tynipano-eustachian fossa 

 and the cbaracters of the columella auris. 



Whatever may be the condition of the parietal ossifications in the 

 very }oung lielodenna, they are in the advdt reptile re()resented 

 solely by a solidly ossified and dense plate of bone. This bifurcates 

 behind, and either limb is directed backwards and outwards and 

 slightly downwards to articulate with the squamosal of the same side 

 as well as with the corresjioiiding jiarotic process. Vievved from 

 above the anterior margin of the parietal plate is represented by a 

 finely serrated transverse line ; the superior surface of the bone is 

 nearly horizontal and usually supports a group of the ossified dermal 

 tubercles, which have fused with it. Near the middle of its ventral 

 surface is seen a small pit, which it would seem is situated too far 

 back to represent the vestige of the parietal foramen. It by no means 

 pierces the bone. At some distance within its external free margin, 

 on either side, this bone develops a longitudinal ridge. This is most 

 conspicuous near its middle, and resting here against its outer aspect 

 are the upper ends of the columella and the prootic. 



In old specimens of this Keptile, the/rontal hones areindistinguish- 

 ably fused together, and upon a superior aspect of the skull not a 

 trace of the median suture that originally stood between them can 

 he made out. And even within the cranium it is hardly to be 

 discerned at all. By a straight transverse coronal suture, this frontal 

 bone articulates posteriorly with the parietal ; while we have already 

 mentioned the fact as to how it is prevented from ])articipating in 

 the furmation of the orbital jieripherv by the meeting of tiie pre- 

 and jiostlVontal elements. Posteriorly, these united frontals are 

 almost entirely masked from our view by the layer of fused and 

 ossified dermal tubercles that overlie the entire fore part of the 

 skull. One never meets with skulls of old individuals of H. sus- 

 pectuin as free from this feature, nor with the naso-froutal and 

 fronto-parietal sutures anything like as clearly defined as is seen in 

 the skull of //. horridum which is figured for us by Mivart 

 (Eucyci. Brit. 9th ed. vol. sx. )). 451, fig. 12 /.). Ventrally, the 

 frontals of the skull of our jiresent subject offer us a peculiar cha- 

 racter. Opposite the orbits each one sends downwards and inwards a 

 broad and curved ])late of bone which mesially meets and fuses with 

 a corresponding jilate coming from the bone of the other side. This 

 arrangement gives rise to a transverse osseous bridge, and the large 

 mesial foramen it assists to form has passing through it certain 



