VERTEBRATES. 



Geotts PHCEBODUS, St. J. andW. 



Phcebodus Sophijg, St. J. and W. 



PI. I, Kg. 14. 



The magnesian beds overlying the coraline limestone of the middle 

 Devonian, in the Cedar valley of Iowa, have afforded, amongst other 

 interesting ichthyic remains more particularly characteristic of the 

 Devonian age, a couple of peculiar forms of minute teeth which unques- 

 tionably belong to that section of the Hybodonts represented by the 

 Cladodi, and of which they are the earliest representatives thus far 

 detected in America. To one of these forms we have given the above 

 generic and specific designations. The other has received the name 

 Bathycheilodus Mclsaacsii. 



The former of the above mentioned forms is represented by very 

 small teeth, the largest of which do nob exceed . 2 inch in lateral 

 diameter and about one-third less in greatest hight, general proportions 

 strong, symmetrical. Base irregularly elliptical in outline, strongly 

 produced in front and faintly excavated at the median line, the antero- 

 inferior angles approximate, and laterally curved to the rounded extremi- 

 ties, broadly though irregularly rounded behind ; the angles in front 

 are occupied by a strong, lateral, pad-like prominence, which is more or 

 less distinctly bilobed and beveled to the deeply excavated inferior sur- 

 face ; posterior margin slightly burled, postero-superior surface mode- 

 rately convex and surmounted by a laterally elongated, well-defined 

 prominence, which is situated nearly midway between the base of the 

 crown and the posterior border to which the surface abruptly slopes, 

 and extending laterally nearly half the diameter of the base. The 

 coronal region consists of three strong cusps, of which the exterior pair 

 are largest, strongly diverging and moderately recurved or nearly ver- 

 tical, antero-posteriorly compressed or suboval in section, apparently 

 without distinct cutting edges, the median cone similar in shape, erect, 

 more or less produced in front and continued to the shallow median 

 depression in the basal border, from the lateral portion of which the 



