VERTEBBATES. 231 



line of the anterior margin. Inferior surface moderately concave 

 longitudinally, and quite strongly arched transversely, meeting at 

 the median line in an obtuse angle, the dense surface layer longi- 

 tudinally striated. Transverse diameter across posterior margin at 

 least 22 mm. ; length along the median line probably 12 mm. ; 

 greatest depth of tooth 6 mm. 



The form first mentioned above, and which is regarded as hav- 

 ing belonged to the upper jaw, presents as typical an example of 

 the genus, as does Copodus cor nut us of Agassiz. It is distinguished 

 from that form by the more regularly arched outline of the anterior 

 margin and the transverse convexity of the crown-surface, in the 

 latter respect bearing greater resemblance to C. spatulatus, Agass., 

 from which, however, it is distinguishable by the more constant pos- 

 terior expansion of the borders of the crown proper. 



The form pertaining to the mandible bears a striking resemblance 

 to the teeth designated under the generic term Labodus, Agass., and 

 which may well be supposed to be homologous with the present 

 form. It differs markedly from the typical species indicated by 

 Professor Agassiz, L. prototypus, from the Irish Mountain limestone, 

 in the relatively great transverse convexity of the coronal surface. 



The discovery of the above species adds another name to the 

 long list of genera common to the Lower Carboniferous formations 

 of the Old and New Worlds. The specific designation is given in 

 honor of VV. C. Van Home, Esq. 



Geological position and localities : St. Louis limestone ; St. Louis, 

 Mo., and Alton, 111. 



COPODUS PUSILLUS, St. J. and W. 



PI. XX, Fig. 1. 



Teeth very small. Form pertaining to the upper jaw subrhom- 

 boidal in outline, lateral borders very gradually converging and 

 somewhat sharply rounded into the slightly arched anterior margin, 

 the worn tooth showing the posterior margin also broadly arched 

 backward. The coronal region is gently and about equally arched 

 in both directions, with a faint narrow depression near the lateral 

 borders, which latter are bordered by ,a narrow fold beveled to and 

 distinctly defined from the basal rim; in front the coronal belt 

 forms a narrow lenticular strip inbeveled to the channeled basal 

 wall, and above the usual lunate triturating area. The coronal 

 surface was enveloped in a dense enamel layer marked by faint 



