35 G PALEONTOLOGY. 



strata are the Goryphodon and Pcdceocyon, respectively repre- 

 senting the ungulate (herbivorous) and unguiculate (carnivor- 

 ous) modifications of the wave-brained section of the class 

 (Gyrencephala) ; their remains have been found in the plastic 

 clay and equivalent lignites in England and France. 



Genus Coryphodon, Ow. — Earely has the writer felt more 

 misgiving in regard to a conclusion based, in palaeontology, on a 

 single tooth or bone, than that to which he arrived after a study 

 of the unique fragment of jaw with one tooth dredged up off the 

 Essex coast, and on which he founded the genus Coryphodon.* 



The marked contraction of the part of the jaw near one 

 end of the tooth seemed, at first view, clearly to shew it to be 

 the narrower fore part of the ramus ; in that case the tooth 

 would have been a premolar, and of comparatively little value 

 in the determination of a genus or species. But a closer in- 

 spection shewed the line of abrasion of the summits of the two 

 transverse ridges of the tooth to be on one side, and the gene- 

 ral law of the relative apposition and reciprocal action of the 

 upper and lower grinders in tapiroid Pachyderms determined 

 that those oblique linear abrasions must be on the hinder 

 side of the ridges. The smaller and more obscure characters 

 carried conviction against the showing of the larger and more 

 catching ones. So, in determining the position of the nautilus 

 in its pearly abode, when the animal without its shell was 

 first brought to England in 1831, the reasons afforded by some 

 small and inconspicuous parts in like manner outweighed the 

 first impressions from more obvious appearances, as well as 

 the bias from the general analogies of testaceous Univalves. 

 Some contemporary naturalists asserted, and for a time it was 

 believed, that the nautilus had been put upside down in its 

 shell, t just as some contemporary anatomists surmised that 



* History of British Fossil Mammals, 8vo, p. 299, figs. 103, 104. This 

 specimen is now in the British Museum. 



f In plate i. of the writer's Memoir of the Nautilus, 4to, 1832. 



