DEVONIAN FISHES OF IOWA 223 



culated ridges, whose course may be either radiating or slightly 

 curved. Lower dental plates moderately convex ; upper plane or 

 slightly concave, with usually about eight costae extending 

 nearly or quite to the postero-internal angle, often radiating 

 from it in fan-shaped fashion (as in the original of Plate VII, 

 fig. 12). 



The dental plates here assembled under the head of a distinct 

 species are among the rarer examples of Dipterine teeth found 

 at the old State Quarry workings in Johnson county, and are 

 seldom perfectly preserved. Two that are rather better than 

 the average have already been figured, but not described, in a 

 memoir on the Devonic Fishes of the New York Formations, and 

 are again illustrated in the present Report (Plate II, figs. 2, 7). 

 The originals of these figures may be regarded as typical of the 

 mandibular and palatal dental series respectively, of the species 

 now definitely established. The same specimens occupy the 

 center of the third row in Plate VII, and adjoining them on 

 either side are other examples of the upper and lower dentition, 

 which may be instructively compared with the types of accom- 

 panying species. The approximate uniformity in size and con- 

 stancy of expression exhibited by all the specimens at our 

 disposal do not permit us to envisage them merely as the young 

 of some other form. Nevertheless, a not remote similarity to 

 the type of D. mordax is not to be denied. 



Formation and locality. State Quarry beds (Upper Devo- 

 nian) ; near North Liberty, Johnson county, Iowa. 



Dipterus nelsoni Newberry. 

 (Plate II, Figs. 11, 11a; Plate VII, Figs. 1-4) 



1887. Dipterus nelsoni H. S. Williams, Bull. U. S. Geol. Surv. no. 41, p. 62, 



pi. 3, fig. 1 (ex Newberry MS.). 

 1887. Dipterus f laeris or D. alleghaniensis H. S. Williams, Ibid., pp. 63, 91, 



pi. 3, fig. 2. 

 1889. Dipterus nelsoni J . S. Newberry, Monogr. U. S. Geol. Surv. 16, p. 89, 



pi. 27, figs. 19-20. 

 1889. Dipterus flabelliformis, laevis, minutus and quadratus, Ibid., pp. 90, 91, 



284, pi. 27, figs. 21-26. 

 1900. Dipterus nelsoni and D. flabelliformis, C. R. Eastman, Journ. Geol. 8. 



p. 37. 

 1907. Dipterus nelsoni and D. flabelliformis, C. R. Eastman, Mem. N. Y. 



State Museum, 10, p. 163, pi. 4, figs. 13, 14. 



