VEKTEBRATES. 93 



DELTOPTYCHIUS PRIMUS, St. J. and W. 



PL V, Pig. 6-8. 



The dentition of the earliest known species, of Deltoptychius is 

 represented in the collections by a few imperfect, fragmentary exam- 

 ples of the posterior forms of the upper and lower jaws, which 

 attain medium size. The mandibular teeth may be distinguished in 

 the examples before us by the obscurer definition of the median 

 prominence from the narrow belt in front, and shallow depth of the 

 enameled abrupt antero-lateral border. The opposed teeth of the 

 upper jaw appear to have had the principal posterior prominence 

 relatively more convex transversely, producing a more rounded out- 

 line in this part of the inner margin than obtains in the repre- 

 sentative Keokuk species. In the proportionate prominence of the 

 secondary lobe, the present teeth bear greater resemblance to the 

 corresponding form occurring in the Warsaw limestone, from which, 

 however, they differ in the greater convexity of the posterior promi- 

 nence. In size the above noticed teeth are uniformly below that 

 attained by the allied forms in the Keokuk limestone, holding in 

 this particular an intermediate position between the latter and the 

 Warsaw species. 



The examples of the above noticed forms thus far known, chiefly 

 from discoveries of Mr. Springer and Mr. Wachsmuth, are few, and 

 unfortunately in a very imperfect state of preservation, owing to the 

 friable nature of the mineralized dental substance ; and while the 

 material is insufficient to enable a detailed description of the teeth, it 

 affords ample evidence of the generic relations, as also indicating 

 the characteristics by which they may be contrasted with congeneric 

 forms. 



Geological position and localities: Upper Burlington fish-bed ; Buf- 

 fington creek, and Augusta, Iowa. 



DELTOPTYCHIUS WACHSMUTHI, St. J. and W. 



PI. V, Fig. 1-5. 



Teeth attaining medium size. Mandibular posterior form triangu- 

 lar in outline, sigmoidally curved along the inner margin, terminating 

 in front in a narrow, inrolled beak ; postero-lateral border gradually 

 converging toward the outer extremity, showing a deep, nearly vertical 

 basal border, slightly inclined outward, and expanded toward the 



