OPTHALMOSAURUS PLBYDELLI. 15 



most marked at the centre. The ventral aspect of the centrum has 

 a distinct longitudinal groove, which is still more distinct in the 

 unfigured and somewhat imperfect specimen. None of the 

 numerous series of vertebrae of 0. icenicus in the collection of Mr. 

 Leeds exhibit a similar ventral channel. It appears that the 

 Gillingham Ophthalmosaurus is specifically distinct from 0. icenicus, 

 and it is equally clear that it is not identical with Ichthyosaurus 

 trigonus or I. ovalis of the Kimmeridge Clay, in which the 

 vertebrae are much larger and relatively longer. Whether, however, 

 it is really distinct from the form described by Phillips from the 

 Oxford Clay, upon the evidence of vertebras, which have never been 

 figured, as /. dilatatus, is, however, not so clear. If, however, the 

 specimens which have provisionally referred to that species on 

 page 30 of the Catalogue of Fossil Reptilia und Amphibia of the 

 British Museum are rightly determined, and that large teeth are 

 always wanting (as in Mr. Leeds' example) from Ophthalmosaurus, 

 it would then appear that the Gillingham form is not identical with 

 /. dilatatus. It is true, indeed, the large imperfect teeth which, 

 from their mode of implantation in the jaw, and evidently 

 Ichthyopterygian, have been found at Gillingham with these 

 specimens, but these may also belong to the owner of the smaller 

 humerus. Under these circumstances, and bearing in mind that 

 /. dilatatus is a very imperfectly defined form, which on that 

 account is perhaps not entitled to rank as a well established species, 

 I propose to provisionally apply a distinct name to the Gillingham 

 Ichthyopterygian, which may be known as Ophthalmosaurus 

 pleydelli. 



