408 MESSRS. HANCOCK AND ATTHEY 



XVIII. — Descriptive Notes on a nearly entire specimen of Pleu- 

 rodus Rankinii, on two new species of Platysomus and a new 

 Amphicentrum, with Remarks on a few other Fish-remains found 

 in the Coal-Measures at Newsham. By Albany Hancock, F.L.S., 

 and Thomas Atthey. (Plates XV., XVI.) 



Pleurodus Eankinii, sp. ined., Agassiz. 



Several years have elapsed since we first obtained specimens 

 of the peculiar little tooth named by Agassiz Pleurodus Rankinii : 

 a few only occurred ; they were found at Cramlington. Since 

 then several specimens of it have been procured at Newsham 

 and Kenton, but never in any great abundance. 



The tooth is, we believe, all that has been known, up to the 

 present time, of this reputed Selachian. In the spring of the 

 year 1870, however, we had the good fortune to meet with the 

 remains of an almost entire specimen of this fish at Newsham, 

 exhibiting a crushed head containing the teeth, most of the body, 

 with thoracic expansions, a dorsal spine, and the shagreen cover- 

 ing or skin (PI. XV., fig. 1). In addition to this interesting 

 specimen, a detached head with the teeth, and a separate spine, 

 have also occurred in the same locality. 



These discoveries are highly important, inasmuch as they seem 

 to demonstrate not only that this species is a Selachian, but that 

 it is a Cestraciont, not far removed from the curious Permian 

 form Wodnika, Munster. This relationship is not only seen in 

 the general characters of the teeth, but also in the similarity of 

 the shagreen and in the form and grooving of the dorsal spine. 



The specimen lies apparently on its belly, and measures a 

 little more than three inches from the front of the head to the 

 posterior tapering extremity of the body, which has lost the tail, 

 and is a little less than two inches wide across the thoracic ex- 

 pansions, which are just behind the head. The contour is much 

 obscured by the scattering of the tubercles composing the shag- 

 reen ; and the slab has been broken away so as to remove a part 

 of the left side of the specimen. A portion of the counter slab, 

 however, has been saved ; and on this the left thoracic expan- 

 sion is sufficiently revealed. The head (PI. XV., fig. 1, a) lies 



