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STRUCTURE AND AFFINITIES OF THE PLATYSOMIDA, 373 
each other, as usual, in the middle line, and on the posterior part of the outer margin 
of each is a small sguamosal or dermal-pterotic (sg.). In front of the parietals are 
rather short /rontals (7) arching over the region of the eye, while forming the two 
posterior-superior margin of the orbit is, on each side, a somewhat triangular- 
shaped posterior frontal or dermal-sphenotic (p.f) placed in front of the 
squamosal, and external to the anterior part of the outer margin of the parietal, 
and the posterior part of the outer margin of the frontal. Immediately in 
advance of the frontals is a narrow elongated median bone (e.). Its posterior 
extremity is somewhat expanded, and presents, behind, an acute angle project- 
ing, wedge-like, into a slight notch between the anterior extremities of the 
frontals, and on each side an obtuse angle, in front of which the bone tapers 
gradually to a point, passing down towards the extremity of the snout. This 
is, without doubt, the median swperethmoidal, and the homologue of that plate, 
which in the Paleoniscide forms the projection of the snout over the mouth. 
Placed on each side of this ethmoid, and articulating with the anterior extremity 
of the corresponding frontal, is another elongated bone (a,f); this is somewhat 
narrow where its posterior extremity joins the frontal, but suddenly it becomes 
expanded laterally, so as to form a prominent angle, directed outwards in front 
of the orbit, from which it again becomes gradually narrowed to a point an- 
teriorly. On its inner margin, near its posterior or upper extremity, is a deep 
round notch, completed into a foramen (n.) by the adjoining superethmoidal, 
and which foramen is clearly the nasal opening, but placed in a rather different 
position from that which it was supposed to occupy by Professor Younec. This 
bone (a,f:) corresponds in position to the anterior frontal of the Paleeoniscide, 
and the nasal openings occupy in reality exactly the same relative position to 
the orbit as in that family, only the great downward development of the bones 
of the nasal region, and the consequent “ prognathous ” character of the face, 
causes them to assume a position remarkably distant from the extremity of the 
snout. The close correspondence of the arrangement with that which has been 
already described in Mesolepis is also quite apparent. In front of the last 
described bones are evident traces of two others, small and narrow, one on 
each side, which apparently sends back its posterior pointed extremity for a 
little distance between the adjacent superethmoidal and anterior frontal. Their 
_ anterior extremities are never clearly exhibited, nevertheless they seem to pass 
down to the extremity of the snout, and to be there placed between the anterior 
extremities of the maxilla. These may be the premaxille, but as yet I have 
seen no teeth upon them. 
A strong parasphenoid bar is seen extending along the base of the cranium, 
and there are also some traces of ossification in the side walls, but, unfor- 
tunately, too indistinct for description. 
The hyomandibular (hm.) is indicated in one specimen as a slender bone 
