789 



PSAM. 



In 



\^ 



H^i /' 



Psammodus ? semicylindricus, Newberry and Worthen, 



.Geo. Sur. 111., Vol. 

 2, 1866, page, 109, 

 plate 11, figs. 4, 4(?, 

 upper surface of 

 profile of a fish 

 tooth somewhat 

 like McCoy's Irish 

 sub-carboniferous 

 P. canalicuLatus^ Brit. Pal. Foss. p. 643, plate 3 g, fig. 12, but 

 without its characteristic plications and its rounded crown. 

 The shagreen-like roughness of the triturating surface is com- 

 mon to several species of this and allied genera; but is only 

 shown where the enamel coating is unworn ; disappearing from 

 long used teeth ; and due to raised rings about the ends of the 

 enamled tubes; evidently intended to prevent the teeth 

 from slipping over the smooth shells which the fish had to crush 

 to feed on the soft enclosed animals ; in worn teeth the rough 

 ness is made by the walls of the tubes. Warsaw, 111. Keokuk 

 limestone. XL 



Psammodus springeri, St. John and Worthen, Geo. Sur. 



111., Vol. 7, 1883, page 202, plate 20, figs. U to 11^ (of which 

 I have only selected the lower set) arranged so as to show the 



