46 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
From the ventral aspect the most conspicuous feature is the large 
flat parabasal, from which project anteriorly and laterally the den¬ 
tigerous premaxillary, vomers, and palato-pterygoids. Posteriorly 
the periotic's and paraquadrates are prominent. Of the primordial 
skull the posterior portion of the trabeculae, the trabeculo-quadrate 
isthmus, the flattened portion of the rods anterior to the ante-orbital 
process, and the basi-occipital arch are visible. 
Only one skull was available for dissection and the bones of this 
proved to be extremely difficult to separate. It was kept in a three 
percent solution of caustic potash for several days with no effect, 
then put into a ten percent solution for several days more, but even 
after this it was impossible to separate the bones, especially the 
frontals and parietals, without injuring them. The material was so 
far from satisfactory that I shall not attempt to give a detailed 
description of the separate bones. The description given has been 
carefully corroborated by study of the cross sections of the head of 
the second specimen. 
Ch o n dr ocran ium . 
The greater part of the chondrocranium consists of two rods 
lying nearly parallel to each another. Anteriorly these are flattened 
and connected by a small isthmus and are covered by the posterior 
two thirds of the premaxillary. Between this region and the eyes, 
the rods are cylindrical, each having on its lateral border a flattened 
triangular process which protrudes laterally from under the edge of 
the frontal, the ante-orbital process. 
In the trabecular region, the rods are very slender but their 
dorso-ventral axis elongates. They diverge slightly and form the 
sides of the brain case. Posterior to this portion, each rod is con¬ 
nected laterally with the quadrate cartilage by a broad, flattened, 
cartilaginous process, the trabeculo-quadrate isthmus. Posteriorly 
the rods articulate with small notches in the parabasal and with the 
anterior border of the otic capsule. 
The parachordal region of the chondrocranium is so closely con¬ 
nected with the bony parts of the otic and occipital region as to be 
indistinguishable from them. The supra-occipital arch appears as 
a short and narrow cartilaginous bridge between the middle thirds 
of the bony periotics. It is also contiguous to the parietals in the 
