408 ICHTHYOSAURUS IN THE MESOZOIC ROCKS OF X.-E. AUSTRALIA, 



been, had that portion of the head mentioned by McCoy as bearing 

 teeth been present ; but the cast in the Museum consists of a 

 portion of the right side included between the posterior margin 

 of the orbit to about half the length of the nostrils, measuring 

 1 foot in length, 1)y 7^ inches high. This portion of the 

 cranium is of course much posterior to that here described, but 

 judging from the relative proportions of the two specimens I 

 am inclined to regard the present fragment as a portion of a 

 species quite as large as Prof. McCoy's, and it is possible they may 

 be identical. But until we know more of these old Australian 

 forms it will be found convenient, for the .sake of distinction, 

 bearing in mind the foregoing facts, to catalogue the present 

 example as Ichthyosaurus Marathonensis. 



The general proportions of this snout resemble those of 

 /. campylodon. Carter, from the English Chalk, and there is 

 present in this species a well-marked vascular channel* along 

 the pre-maxillary and dentary bones, just as we see it here. 

 Describing this, Sir Richard Owen says — " Opposite the origin 

 of the inner alveolar plate the pre-maxillary is traver.sed by a 

 straight longitudinal groove, 4 lines in breadth, which contracts 

 as it advances forwards."! Touching the similar groove seen along 

 the dentary, he adds — "The outer part of the dentary at the 

 hinder fracture is 6 lines in thickness, smooth and convex on its 

 outer side, which is traversed by a longitudinal groove, which also 

 slightly narrows as it advances." 



As well as in /. campylodon, this groove is shown in Prof. 

 Owen's figures of the jaws of /. communis^ and /. plalyodon, § 

 Liassic species. 



McCoy notes the resemblance of the teeth of his /. Australis to 

 those of /. campylodon previously referred to, a likeness which is 

 also perceptible in our species. I am unable, however, to institute 



* Mon. Foss. Rept. Cret. Form. 1851, t. 25, fig. 1 g, 

 t Loc. cit., p. 75. 



t Mon. Foss. Rept. Liassic Form, t 24, f. 2. 

 §Mon. Foss. Rept. Liassic Form. t. 31, f. 2. 



