82 S. W. Williston. 
Two of these bones have been lost in all modern reptiles, and, with 
the exception of the Squamata, three of them. We have generally 
assumed that the supraoccipital and epiotic of the stegocephs are 
these two, but I question very much, in the light of the evidence fur- 
nished by Labidosaurus, whether this assumption is justified. I 
have long believed that the small element intercalated between the 
paroceipital and the so-called squamosal of the lizards corresponds 
to the epioties of the stegocephs, and I am further confirmed in this 
opinion by the position and relations of the bones in Labidosaurus. 
However, my views as to the homologies of the cranial arches have 
been not a little shaken by the structure of the labidosaurian and 
pelycosaurian skulls, and I shall not venture here to offer any very 
decided opinions, preferring to wait until further evidence is avail- 
able, especially that to be yet furnished by the skull of the Diadec- 
tide. 
In the remarkable genus described by Cope and Case as Hdapho- 
saurus a pair of bones almost certainly homologous with those here 
provisionally called the “postparictals” are identified by Case as the 
epiotics, but with a query.8 In the only known specimen of the 
genus, the type, these bones and the parietals were crushed down 
over the supraoccipital nearly to the foramen magnum, and this, I 
believe, was their normal position. In the restoration given by Case, 
however, they have been elevated nearly to the top of the supraoc- 
cipital, depressing the paroccipitals so far that their outer extremity 
ends near the articular end of the quadrate. In all probability it 
articulated, as in Labidosawrus, with the outer end of the so-called 
epiotics, or the inner end of the “quadrato-jugals,” as in Labido- 
saurus. The relations of all these bones, the “epioties,” “quadrato- 
jugals,” quadrate and paroccipitals appear to be quite the same in 
Dimetrodon, Edaphosaurus, and Labidosaurus, and I doubt not that 
they are all homologically identical. In Hdaphosaurus, however, 
another bone is recognized between the parietal and prosquamosal, 
clearly corresponding with the additional element supposed to occur 
in Labidosaurus, but which I cannot find. Should it be a distinct 
element in either or both these genera it does not in the least cast 
®Pelycosauria, p. 151. 
