30 FAUNA OF THE CORNBRASH. 



Skiatype. — " The teeth are distinguished solely by their generally more 

 stumpy form, and by the fineness of the surface-pores of the crown, which is 

 only just reticulated near the edges, and by the folds being finer and closer than 

 those of the other species." This definition is supplemented by A. S. Woodward 

 in distinguishing the different series. In the most posterior series the teeth 

 are small and oval, with very coarse superficial reticulations. In the fourth 

 they are relatively broad and flat; in the third somewdiat longer, the postero- 

 lateral angle gently upturned and the anterior third slightly bent forwards 

 and downwards ; in the second they are broadest posteriorly, with an abrupt 

 hinder margin, the antero -lateral angle produced and the postero-lateral angle 

 rounded; and those of the first series are still smaller and apparently shorter. 



Description. — It will be seen that species of Strophodont teeth are very 

 difficult to be distinguished by their shape ; reliance must be placed on the character 

 of their ornament and reticulations. In many cases they are not to be dis- 

 tinguished from those from the Stonesfield Slate. Some of them belong to one of 

 the later series of teeth and some to those of the earlier ones. 



Distribution. — Of these teeth, twenty-two are from St. Botolph's Bridge, near 

 Peterborough, in the Sharp collection now in the British Museum, of which 

 thirteen belong probably to series 1 and 2, and the remainder to series 3 and 4 ; 

 also from Rushden and Shipton-on-Cherwell ; from Polebrook ; and from 

 Thrapston and Stowe in other collections. That is to say, they only occur 

 where the Cornbrash is underlain at no great distance by calcareous rocks 

 from which they might have been derived, which is rendered not impossible 

 by their abundance in the Neocomian beds in a remanie form. 



Strophodus tenuis, Agassiz. Plate I, figs. 7 a, b, 9. 



1838. Strophodus tenuis, Agassiz, Poiss. Foss., vol. iii, p. 127, pi. xviii, figs. 16 — 25. 

 1889. — A. S. Woodward, Cat. Foss. Fishes, B. M., p. 317. 



Skiatype. — This species of tooth differs from 8. magnus by being slender and 

 elongated and having a tendency to rise into a protuberance in the posterior por- 

 tion. Though smaller than S. magnus, its surface has a less delicate reticulation 

 and the pores are more masked. The elevated anterior teeth have their ends 

 much pushed in. According to A. S. Woodward, the first three rows of teeth are 

 all much arched, and the superficial coronal ornament is as in S. magnus, except 

 the anterior teeth. The hindermost teeth are small and oval, those of series 4 

 gently rounded; those of series 3 are much longer, the crown raised towards 

 the anterior end and bent downwards and forwards in front; those of series 2 

 are much elevated mesially, slightly keeled and narrowed at each extremity; 



