The Skull of Labidosaurus. 
“I 
or 
examination with a lens. I am satisfied that there is none, that there 
is but a single bone here and not two, and this conclusion was 
reached before I perceived its significance in comparison with the 
skull of Dimetrodon. ‘This large, flat and thin, or gently convex 
bone unites on its inner side with the parietal, on the front side with 
the postfrontal and postorbital, and on the lower or outer side by a 
very squamous and loose suture with the posterior prolongation of 
the jugal. This is precisely the arrangement of these bones in 
Dimetrodon, and I am satisfied that the elements are morphologically 
‘dentical. The chief difference between Labidosaurus and Dumet- 
rodon consists in the rather large vacuity of the latter piercing what 
otherwise would be the squamosal, jugal and postorbital bones. For 
the present I accept Case’s determination of the squamosal element 
as the prosquamosal, but I feel far less assured of its homology than 
I did formerly, though I doubt not that it corresponds quite with 
the element in the ichthyosaurs originally named prosquamosal by 
Owen. 
On the posterior or occipital side there are two cranial roof bones 
on each side, clearly and positively shown in all our specimens, one 
bordering the hind margin of the parietal, the other the squamosal, 
and called by Cope respectively the supraoecipital and the tabulare, 
that is the so-called epiotic of authors. They differ from the bones of 
the upper surface of the skull in lacking the superficial markings 
or pittings, and are suturally united with the superior bones at an 
angle of nearly ninety degrees. The superior or inner of these 
two pairs of bones, those bordering the parietals, the supraoccipitals 
of Cope, are the narrower of the two. Their inner ends are curved 
downward slightly, with an angular interval between them into which 
fitted the small spine of the real supraoccipital described further on. 
It has long been believed that the so-called supraoccipital of the 
Stegocephala and of those reptiles in which a like bone is believed to 
occur does not correspond to the true supraoccipital of the higher 
reptiles and mammals. They are clearly membrane bones, and have 
been called the postparietals by Broom. That they are not the real 
supraoccipitals is very evident in this specimen in which a large 
and well defined supraoccipital is found quite dissociated from the 
