AN ICETHYOSAUEIAN SKULL FIWM QUEENSLAND.— LOXGMAN. 247 



On the upper part of the skull the elongate premaxillae can be traced back 

 for a distance of 615 mm. to the narial openings. Between these two bones in the 

 superior surface is a well-marked symphysial groove. The nasals are exposed from 

 beneath the premaxillse at about the anterior third of the length of the skull, and 

 at first are on a lower plane than the hemispherical suj^erior borders of the diverging 

 premaxillae, forming a triangular recess. Further back there is a secondary 

 triangular depression, the borders of which are parallel to the anterior recess, but 

 this is entirely internasal. Lateral divisions of the nasals extend outwards beyond 

 the frontals towards the superior border of the orbits. Sutures Avith post frontals 

 cannot be traced. 



The external narial openings can be seen on both sides, but they are distorted. 

 A semicircular raised border is present behind the openings. Incomplete maxillae 

 are present, but the sutures between them and the lachrymal bones and the jugals 

 cannot be positively traced on either side. 



In the region of the frontals a remarkable rectangular raised process was 

 present in the undisturbed fossil. On careful development this proved to be mainly 

 matrix closely investing a troughlike depression, with raised lateral borders, as 

 may be seen in Plate XV. At first this was thought to be a veritable raised bony 

 border surrounding the pineal foramen, and suggesting an unusual development of 

 " the third eye,'' but the true foramen is apparently situated in a more posterior 

 position. This closely adpressed structure consists of two parallel bars, thinly 

 joined anteriorly ; the bars are 90 mm. in length and are symmetrically disposed 

 at a distance of 10 mm. from the median line. If this structure is actually in situ, 

 which seems unlikely, it would demand generic recognition. The frontal bones 

 evidently do not extend far beyond the area of this structure. In view of the partial 

 disorganization of the specimen, possibly associated with an attack from other 

 predaceous or scavenging monsters of the period, it is suggested that this curious 

 structure represents an inverted cranial element. It cannot, however, be allocated 

 with any of the bones, the contours of which are so clearly demonstrated by 8ollas' 

 classic sections,^ and possibly represents hyobranchial elements. And it is, of course, 

 possible that further material will demonstrate characters which will warrant the 

 establishment of a new genus for this large Australian Ichthyosaur. The prominent 

 ridges, which are present in the parietal region and on the nasal bones, appear 

 to be distinctive features. From the occipital border of the parietal region a con\^x 

 median ridge extends anteriorly, and this is accentuated by the presence on each 

 side of elongate valleys, the lateral sides of which curve upwards to form the 

 borders of the supra temporal fossae. At the anterior termination of the median 

 ridge there is a cavity which could not be traced into the internal tables of the 

 skull, but which probably represents a disrupted pineal foramen. This is nearly 

 in line with the anterior borders of the supratemporal fossae, and is thus in the 

 usual position for the foramen. 



3W. J. SoUas, Phil. Trans. Roy. Soc, B, 208, 1916, pp. 66-126. 



