AND AFFINITIES OF PTYCHODTTS. 



131 



naturalist of so much knowledge as Agassiz. There was a fine 

 series of specimens of Ptycliodus in the Woodwardian Museum at 

 Cambridge ; but although these showed the linear and parallel 

 arrangement of the teeth and apposition of the jaws, and although 

 the method of wearing resembled that of the Hays, the subject 

 had not been dealt with by any one so clearly as the examples in 

 the Brighton and British Museums had been worked out by Mr. 

 Woodward. At the same time Prof. Seeley thought there was still 

 some question if Ptycliodus was really a Skate. It was certainly 

 the type of a peculiar plagiostomous family. 



Mr. Newton pointed out that if the arrangement suggested by 

 Mr. Smith Woodward was correct, the large teeth of the lower jaw 

 ought to be worn on both sides, and those of the upper jaw on the 

 inner side. 



Mr. Lydekker said he had described a dental plate of a Myliobatis 

 from the Eocene of India which appeared to show an approxima- 

 tion in its contour to Ptycliodus. 



Dr. H. Woodward had not seen the Cambridge specimens, but 

 noticed the very fine example from Brighton ; the specimen now 

 exhibited showed portions of the teeth of both jaws well preserved. 

 He pointed out the absence of the Cestraciont prehensile teeth, and 

 their replacement by crushing-teeth in Ptycliodus. This was a 

 most important observation of Mr. Smith Woodward's. He thought 

 the present discussion would throw some light on the peculiar 

 crushing-teeth of Carboniferous Sharks. 



The Author, in reply, said that in the paper he had treated the ques- 

 tion of attrition. The lower median teeth were worn not only on each 

 side, but also on the summit. The evidence at present seemed to 

 him to leave it doubtful whether Ptycliodus was the type of a new 

 family or not. He agreed with Dr. Woodward that forms like 

 Psammodus would have some light thrown on them by investigations 

 into the dental arrangement of Ptycliodus. 



* 



