2 8 E. B. BRANSON 



Deltodus complanatus Newberry, 1897 (Transactions of the New York Academy 



of Science, Vol. XVI, p. 298, Plate XXIV, Figs. 1-7). 

 Deltodus occidentalis Eastman, 1903 (Bulletin of the Museum of Comparative 



Zoology at Harvard College, Vol. XXXIX, p. 200, Plate 4, Fig. 38, and 



Plate 5, Fig. 53). 

 Sandalodus complanatus Eastman, 1903 (ibid., p. 198). 



Teeth triangular in outline. In teeth of average size, 4o-6o mm long, postero- 

 lateral border about i cm longer than antero-lateral. The outer end terminates 

 in an acute point; the inner end has the inner angle obtuse, the outer angle acute. 

 Tooth slightly arched longitudinally and transversely, but, as compared with 

 associated species, flat and thin. A low, broad ridge extends from the obtuse 

 angle of the inner end to the outer end. From this ridge the surface declines very 

 rapidly to the thin antero-lateral border and gently toward the postero-lateral 

 border. Alation broad, slightly upturned. Enameled surface smooth and pol- 

 ished, everywhere finely punctate. Lines of growth usually not well marked. 

 Antero-lateral border not modified for articulation with other teeth, usually 

 straight or slightly convex. 



S. occidentalis differs from D. spatulatus in being much less arched 

 both longitudinally and transversely, and in having the ridge, which 

 is not as high as in D. spatulatus extending from the obtuse angle 

 to the outer end very close to the antero-lateral edge, instead of at 

 some distance from it, as in D. spatulatus. The surface of the tooth 

 declines rapidly to the antero-lateral border from the top of the ridge, 

 and gently toward the postero-lateral border, while in D. spatulatus 

 the stronger slope is toward the postero-lateral border. Antero- 

 lateral margin not concave, as it is in D. spatulatus. 



This species is referred to Sandalodus because there is evidently 

 only one tooth to each ramus of the jaw. As has been stated, the 

 large teeth have no articular edge, and although they are numerous 

 in the Burlington limestone, no teeth have been found that could 

 occupy the position of the median or anterior teeth as present in the 

 dentition of Deltodus, Cochliodus, and Psephodus. 



In examining a large number of fragmentary teeth of Sandalodus 

 complanatus and Deltodus occidentalis, it was found impossible to 

 distinguish one species from the other, and, after examining more 

 than a hundred well-preserved teeth, the conclusion was reached 

 that the two groups of teeth represented a single species. In large 

 collections they grade into each other to such an extent that it is 

 impossible to separate them, but it is not difficult to understand 



