THE DEVONIAN ROCKS OF CANADA.' 85 



from this poiut of view the mandibular rami are elongated, comparatively narrow 

 and more or less pointed at both ends. As viewed laterally, their npper and tooth- 

 bearing margins are nearly straight, their lower borders gently convex, and are deepest 

 or broadest near the midlength. The anterior termination of both jaws is well seen, but 

 in profile also, in a specimen to which reference has been made on page 82. In this 

 specimen the lower jaw curves obliquely upwards at its anterior termination, and is 

 slightly overlapped by the somewhat recurved apex of the upper jaw, which latter pro- 

 jects a little beyond the lower jaw in front. Posteriorly, and in a profile view, each of 

 the mandibular rami extends just as far backward as to the postero-inferior termination of 

 the prsBoperculum. In specimen No. 2 the lower jaw is displaced, isolated and crushed 

 down in such a way as to shew the whole of the under and a considerable portion of 

 the iufero-lateral surfaces of both of the rami of which it is composed. As seen in this 

 specimen, the two mandibular rami are A'-ery stout, and diverge outward and back- 

 ward in a gentle curve from the symphysis. They widen gradually backward and for- 

 ward, and at their rather broad posterior terminations, are rather deeply and suban- 

 gularly notched near the centre, apparently for articulation with the quadrate, and 

 divided thereby into two processes, of which the inner one, which probably represents 

 the condyloid process, is longer, broader and more rounded posteriorly than the outer 

 one. Although the dentary, articular and angular elements are evidently well developed 

 in each ramus of the lower jaw of Eusthenopteron, the exact limits of these elements cannot 

 be defined in any specimen known to the writer, and no trace of the splenial has yet 

 been detected. In a full side view, the lower jaw of Evsthennpteron, with its teeth, is 

 singularly like that of the Asierolepis of Hugh Miller (but not of Eichwald), as figured in 

 the " Footprints of the Creator," but as seen from below, the same jaw bears an equally 

 close resemblance to that of Dipterus as illustrated by Hugh Miller in the same volume. 

 On the under surface of the head, the space between the mandibular rami is filled 

 by two long and rather slender jugular plates, which are very acutely pointed in front 

 and narrowly roirnded behind. In Eusthenopteron, as in Tristichopterus, no traces can be 

 detected of an azygos jugular j)late, or of any small lateral plates. 



Dentition. — The outer row of teeth upon the premaxillary portion of the frontal 

 plate has already been partially described in connection with that plate. The two 

 maxillae of the upper jaw and the presumably dentary region of each of the mandibular 

 rami of the lower, are each armed with an outer row of very small and closely arranged, 

 but not quite equidistant teeth, and with an inner row of much larger ones, which are 

 placed at comparatively wide intervals apart. The small outer teeth are conical, and 

 slightly curved. To the naked eye they appear perfectly smooth, but under a powerful 

 simple lens they are seen to be faintly and longitudinally striated. The large inner teeth 

 are also conical in form, Imt strongly compressed, and they are also longitudinally 

 grooved. In specimen No. 4, which, however, is obviously not more than half grown, 

 there are two comparatively large teeth, about six millimetres in height, besides many 

 much smaller ones, on the right rainus of the lower jaw. The first of these large teeth 

 is placed at a distance of about thirteen millimetres from the anterior termination of the 

 ramvis, and the second about fifteen millimetres from the first, but in this particular 

 specimen some of the larger and inner teeth have evidently been displaced and are lying 



