SIR R. OWEN ON A LABYRINTHODONT AMPHIBIAN. 335 
interblending of the dental tissues complementary to and confirm- 
ative of the batrachian modifications exemplified by the recovered 
bones of the skull. 
As shown by the figure 1 of Plate XVI., the upper surface of the 
skull is nearly flat, the feeble convexity, transversely, of the outer 
third parts gradually falling to as feeble a concavity at the middle 
third. The exposed surface of the bones is sculptured according to 
the pattern which I have termed “rhytidoganoid” in Brachyops. 
The forwardly converging lateral borders are rounded off into an 
obtuse fore end, two inches broad about an inch behind that end. 
The rami of the mandible converge, corresponding with the denti- 
gerous borders of the maxille, and seemingly coalesce to form a 
flattened symphysial end of the lower jaw, having a transversely 
convex termination fitting into that of the overlapping upper jaw 
(Plate XVII. fig. 1, & Plate XVI. fig. 2), the animal having become 
fossilized with its mouth close shut. 
The fore end of the upper jaw is formed by the premaxillaries 
(22,22); their medial suture is 38 millim. in length; the bones 
extend laterally backward to contribute to the front border of the 
outer nostril (n, figs. 1 & 2, Plate XVI.), above which they terminate 
in a point. The pattern of their external sculpturing will be pre- 
sently described. 
The maxillaries, 21, 21, contribute the smallest portion to the 
upper surface of the skull, where it forms part of the upper border 
of the nostril. Only on a side view, as in fig. 2, Plate XVI., can the 
due extent of the outer surface of the maxillary be seen, and the 
proportion, », it contributes to the under and hinder border of the 
nostril, whence it extends backward with a decreasing vertical 
diameter to beneath the orbit 0. Returning to the upper surface of 
the skull (Plate XVI. fig. 1), the nasal bones 15, 15, there show 
their great expanse and triangular shape: their extreme length is 
34 inches (90 millim.), and that of their mid suture is 24 inches (63 
millim. Each nasal expands as it recedes from the premaxillary, 
and contributes about one third of the upper border of the nostril, 
beyond which the bone unites with the maxillary, 21, and thence 
extends further back to terminate in a point wedged between the 
frontal, 11, and prefrontal, 14. The frontals, 11, retaining their mesial 
suture, form together a subquadrate plate with the anterior angles 
rounded off; the posterior ones are truncate: the connexions of 
these bones are, anteriorly, with the nasals, laterally with the pre- 
and postfrontals. The parietals, with which they unite behind, 
are represented by fragments, the occipital part of the skull being 
lost. The prefrontals, 14, are mesially united with the nasals, the 
mid frontals and postfrontals; laterally, with the maxillaries, 21: 
they form the anterior and part of the upper border of the orbits. 
Of the poséfrontals, 12, only the angle j jonas and wedged between 
the mid and prefrontal i is preserved. 
The roof of the portion of skull formed by the above-noted bones 
is almost flat, of subtriangular figure, with the anterior apex rounded 
of. The outer nostrils, x, come partially into view, the orbits, o, 
242 
