VERTEBRATES. 63 



but prominent earinae. From these spring a great number of 

 simple or branching secondary ridges, which spread over all 

 the surface of the crown. These ridges are sharp and well 

 denned, and are separated by obtuse furrows of about double 

 their width; both ridges and furrows highly polished and uni- 

 formly punctate. 



It unfortunately happens that this remarkable species is represented in the 

 collection by a single specimen only, and that a fragment, a portion broken 

 from the centre of the tooth ; the margins being gone, carrying with them all 

 data for determining its size or form. It is evident, however, that it must have 

 been equal if not superior in size, to any other tooth in the collection. At 

 least 2 inches wide in its narrowest part. The microscopic structure and style 

 of ornamentation are very similar to those of the large and beautiful teeth 

 described by Agassiz. (Poiss. Foss* Vol. 3, p- 97, Atlas, Vol. 3, Tab. \\,fig. 

 5-9), under the name of Orodus ramosus, and it is not improbable that we have 

 in this fragment the central cone of the tooth of a species of Orodus, perhaps 

 generally similar in form to 0. ramosus, but considerably larger and more 

 highly ornamented. 



Figures 13, 13 a, are top and side views, natural size. 



Formation and locality: Kinderhook group, "Goniatite bed," Rockford, 

 Indiana. 



Orodus plicatus, N. and W. 



PI. IV, Fig. 5. 



Teeth small, laterally elongated, slender, somewhat arched; 

 crown bearing a sub-medial prominent cone, with 4 or ^lateral 

 ones. The central cone is rounded, sub-acute, its summit 

 marked by numerous fine radiating striae. On either side a 

 beaded crest runs down to and over the lateral cones; lateral 

 cones small, not crowded, from their summits one or two promi- 

 nent, acute, divergent costas, descend on either side to the base 

 of the crown, much stronger on one side than the other ; base 

 of the median cone and the entire surface of the lateral por- 

 tions of the crown on one side, ornamented with numerous, 



