122 



ME. A. S. WOODWARD ON THE DENTITION 



curious " Ichthyodorulites " also armed the dorsal fins of the same 

 fish. 



Owen's further evidence in a similar direction consisted in the 

 remarkable resemblance between the medullar} 7 tubes traversing the 

 dentine of the teeth and those to be observed in the teeth of Ces- 

 tracion and Acrodus ; and in this particular it became obvious that 

 there was a marked divergence from the dentinal structure of 

 Wiynchobatus (Mhina) *, with which the peculiarities of mere 

 external form suggested comparison. 



The latter superficial resemblance has frequently been noted by 

 subsequent writers f , and Dixon has even remarked $ upon the 

 possibility of the genus Wiynchobatus affording some clue to the 

 arrangement of the fossil teeth in the jaws. But until eleven years 

 ago the three fundamental arguments of Agassiz and Owen remained 

 unshaken, and it is only within this later period that comparatively 

 satisfactory materials for study have been forthcoming. Professor 

 E. D. Cope was the first, in 1875 §, to show that the supposed dorsal 

 spines of Ptychodus were really the paired fins of Teleostean fishes, 

 having discovered much more complete specimens in the Cretaceous 

 beds of the Western Territory of Kansas. And last year, in the 

 pages of ' Science Gossip ' |J, I was able to demonstrate briefly that 

 the fossils upon which Agassiz based his conclusions as to the 

 arrangement of the dental armature were likewise misleading, and 

 that there was not the slightest agreement with the Cestraciont 

 plan. 



As regards microscopical structure, it seems possible to draw con- 

 clusions from Owen's observed facts somewhat different from the 

 original inferences still generally accepted. And it is with a dis- 

 cussion of the two latter questions, especially the first named, that 

 the present communication is particularly concerned. 



In the prosecution of such an inquiry the fossils in the National 

 Collection afford several important fragments of evidence, and of 

 these it is proposed to offer some detailed descriptions. But the 

 most beautiful and instructive specimen that I have the honour of 

 bringing before the notice of the Society forms one of the fine series 

 of Cretaceous fossils in the Brighton Museum, collected by Henry 

 Willett, Esq., F.G.S. To the latter gentleman I owe my best thanks 

 for the opportunity of studying it in London and of utilizing it in 

 the present investigation ; and I have also to acknowledge much 

 kind help from Edward Crane, Esq., F.G.S., Chairman of the 

 Brighton Museum Committee, who first pointed out to me the fossil 

 last spring. 



* ~R. Owen. ' Odontography,' pp. 44-46, pi. xxiv. 



t e.g. Pictet (' Paleontologie,' 2nd edit. 1854, vol. ii. p. 265) and Quenstedt 

 (' Handb. der Petrefaktenkunde,' 1st edit. 1852, p. 181). 



\ F. Dixon, ' Geology and Fossils of Sussex,' 1850, p. 361 ; 2nd edit., 1878, 

 p. 390. 



| E. D. Cope, " Yertebrata of the Cretaceous Formations of the West" (U. 

 S. Geol. Surv. Terr., 1875), pp. 244 a-f. 



|| Smith Woodward, " Chapters on Fossil Sharks and Eays.— IV.," 'Science 

 Gossip,' vol. xxi. 1885, p. 109. 



