PISCES. 81 



mian period (see ante, p. 17). Such must also be the case with 

 many of our Upware specimens. On the other hand these palatal 

 teeth shew no specific differences from those of S. gigas, Ag. from 

 the Kimmeridge clay, nor do I think they could be distinguished 

 and separated out if they were found mingled together. The fact of 

 the undoubted occurrence of many Jurassic species in the Upware 

 deposit affords good ground for the belief held by MM. Walker, 

 Teall and others, that these are truly ' derived ' fossils 1 . 



Under these circumstances I record both species, native and 

 derived, from Upware, the proper Neocomian ones being, in my 

 opinion, especially well witnessed to by the number of the specimens, 

 and the scantiness of phosphate of lime either in their present 

 mineral substance or in the form of concretions around the roots of 

 the teeth. 



SPILERODUS NEOCOMIENSIS, Agassiz. 

 (Plate i. fig. 4 a c.) 



Sphcerodus Neocomiensis, Agassiz, 1843. Poissons Fossiles, n. 



2, p. 216. 



Pictet and Campiche, Palceontologie 



Suisse, St Croix, Vol. i. p. 72, pi. 9, 

 f. 16. 



We have already pointed out the resemblance of the teeth of 

 this species to those of P. gigas of the Kimmeridge clay. MM. 

 Pictet and Campiche write : " Je suis meme tres-embarrasse pour 

 y trouver des differences apprdciables," but add that perhaps the 

 cap formed by the dentine and enamel is deeper and narrower in 

 S. gigas. 



These teeth are always isolated, and at Upware and Brickhill 

 only the palatal type is known ; but at Potton the sharper cutting 

 incisor teeth are also found. Fragments of the jaw-bone occasionally 

 occur still adhering to the tooth, but usually dentine and enamel 

 only remain when the under side is cupped, and in some specimens 

 the dentine also has disappeared, leaving only the saucer-like 

 enamel cap, shaped like an acorn cup. These palatal teeth were 

 known as ' buttons ' amongst the workmen, for whom they were 



1 As mentioned before, I have no knowledge of any specimen of Spluerodus gigas 

 or Rtrophodus reticulatus having been found in the Jurassic rocks of this neighbour- 

 hood (Cambs. and Bucks. ). 



K. 6 



