pisces. 165 



1902. Onychodus sigmoides Hay, Bull. U. S. Geol. Surv., 179, p. 363. 

 1908. Onychodus sigmoides Eastman, Iowa Geol. Surv., 18, pi. 1, figs. 4, 11. 

 1908. Onychodus sigmoides Eastman, New York State Museum, Memoir 10, pi. 1, 

 fig. 3; pi. 3, fig. 2. 



Newberry' s description— "Fishes of large size; head at least eighteen inches long, 

 composed of numerous angular and rounded plates, supported on a cartilaginous brain- 

 box, and so imperfectly united that in the fossil state they are usually disconnected and 

 scattered. Of the head plates, the operculata are from three to five inches in diameter, 

 nearly circular, but with a produced anterior angle. The maxillaries are triangular in 

 outline, the anterior and posterior angles much produced, the lower margin nearly 

 straight, and set with a large number of conical, pointed teeth. The dentary bone of 

 the mandibles is often more than a foot in length, curved gently upward at its anterior 

 extremity, which is rounded. Its posterior extremity is thin and flattened running off 

 to a pointed edge, where it was overlain by the articular portion of the mandible. 



The upper margin of the dentary bone is thickly set with conical, pointed teeth. 

 Embraced within the anterior extremities of the mandibles is an arch of bone, which 

 supports a series of large, conical, sigmoidally curved teeth seven or eight in number, 

 set vertically, and projecting downward, forward and upward. These teeth show several 

 prominent roots, which partially embrace the bases of the adjacent teeth. The ex- 

 terior surfaces of the cephalic plates and the exposed portions of the maxillaries and 

 mandibles are thickly set with small enameled tubercles, which have the form of ap- 

 pressed, striated, or sulcated cones. The body was covered with relatively thin, highly 

 ornamented scales. These have a circular or elliptical outline; the under surface is 

 smooth, or faintly marked with concentric lines, and often bears a central elevated tuber- 

 cle or ridge. The exterior surface shows an anterior semi-lunar space, occupying about 

 half its area, where adjacent scales were superimposed. Th,is space is comparatively 

 smooth, but is delicately ornamented with radiating lines of pits. The posterior and 

 exposed portion of each scale is roughened with appressed, striated tubercles, similar 

 to those on the cephalic plates, and with branching, somewhat foliated ridges of enamel." 



Remarks — Two sigmoidal teeth have been collected from the Grand Tower lime- 

 stone of southeastern Missouri, but they are complete enough to make the identification 

 satisfactory. Two specimens have been collected from the Callaway limestone of 

 Moniteau County. 



Unidentified fish remains 



Fragments of bone indicate the presence of other fishes besides Onychodus sigmoides 

 Newberry, but the fragments are too imperfect for generic identification. 



