DEVONIAN FISHES OF IOWA 



115 



slightly waved, delicately crenulate or tuberculate costae, which 

 pass with a very slight obliquity over the face of the spine, this 

 obliquity increasing toward the base as well as toward the an- 

 terior margin, Where the ridges are also somewhat coarser and 

 more widely separated than either distally or posteriorly. A 

 noteworthy feature of these ridges is that they terminate before 

 reaching the anterior margin, leaving a smooth and highly pol- 



Fig. 17. Gyraeanthus primaevus, sp. nov. Stafford limestone (Marcellus division of the 

 Erian) ; Stafford, New York. Lateral aspect of fln-spine, x 3-2. 



ished enamelled band adjacent to the front margin or cutwater. 

 As many as 22 of these ridges terminate along the oblique line 

 of insertion, and here the evidence of minute tuberculation is 

 more distinct than in the more distal portion. About midway 

 the length of the spine an imperfect division or branching of 

 the costae is to be observed. How far the internal cavity is open 

 along the posterior face cannot be ascertained, but the oblique 



