OSTEOLOGY, ETC., OF SYXGNATHUS PECKIANUS. 627 



velops apparently in a manner similar to what occurs in the 

 placoid scales of the body, from the membranous plate already 

 spoken of; and (2) an ectosteal portion, which may be termed 

 the auto-supra-occipital. The supra-occipital is somewhat 

 narrowed in front, projecting between the posterior portions of 

 the frontals. 



Laterally from this bone we have on either side the parie- 

 tals (Pa.), small bones which do not meet in a sagittal suture, 

 but are separated throughout their entire length by the supra- 

 occipitals, as in the pike and the salmon. Anteriorly they 

 articulate with the frontals. The name dermo-epiotics, 

 which Bridge has suggested for these bones in Amia,^ is here 

 very applicable, for they directly overlie the epiotics, appearing 

 like a parostosis formed upon these bones. 



The pterotics (Pt. O.) extend far forward to a point just 

 behind the sphenotics, and form, along with the pro-otics and 

 sphenotics, the articulating surface for the hyomandibular. 

 They descend pretty well to the base of the skull, their poste- 

 rior parts overlapping the anterior lateral portion of the 

 basi-occipital, and articulating with the exoocipitals. They 

 form the lateral boundaries of the membranous space in front 

 of that bone. Anteriorly they articulate with the pro-otics. 



These bones (fig. 9, Pr. O.) bound the membranous space in 

 front, and extend forward nearly to the anterior limit of the 

 postorbital region of the cranium. They extend only slightly 

 upwards on the sides of the skull to articulate with the pterotics 

 and sphenotics, and unite across the middle line of the skull 

 anteriorly, but are separated posteriorly, leaving a space closed 

 in only by the parasphenoid. At the sides in this region are 

 the sphenotics (Sp. O.). There seem to be no distinct ali- 

 sphenoids, the part of the skull having the usual relations of 

 these bones being ossified by the pro-otics. There is apparently 

 also no basisphenoid. 



The frontals (fig. 8, Fr.) are membrane bones of compara- 

 tively large size, extending from the parietals posteriorly to 



1 T. W. Bridge, " The Cranial Osteology of Amia calva," ' Jouru. of Auat' 

 aud Phys.; vol. xi, 1877. 



