220 IOWA GEOLOGICAL SURVEY 



phalus" bed, which lies about eight feet below the summit of 

 the Middle Devonian in Muscatine county. 



Formation and locality. Cedar Valley limestone; Fairport, 

 Muscatine county, Iowa. A description of the local section 

 whence the holotype was obtained is given by Professor Udden 

 in the Annual Report of the Iowa Geological Survey for 1898 

 (IX, p. 283). 



k 



Dipterus costatus Eastman. 



(Plate II, Fig. 8) 



1900. Dipterus costatus C. R. Eastman, Journ. Geol. 8, p. 39, text-fig. 4. 

 1907. Dipterus costatus C. R. Eastman, Mem. N. Y. State Mus. 10, p. 161, pi. 

 4, fig. 9. 



Dental plates agreeing in size and general outline with D. 

 calvini, but having fewer and more widely separated coronal 

 ridges, which disappear before reaching the middle of the plate. 

 The distinguishing feature of this species consists in the elevated 

 acute ridge extending along the entire length of the inner border 

 and separated from the remaining tuberculated ridges by a broad 

 longitudinal furrow. This ridge appears to be made up of three 

 coalesced costae, of which the third counting from the inner 

 margin is the largest. The two innermost costae are so faint 

 as to be almost imperceptible against the steep face of the main 

 ridge. The latter shows no evidence of having been tuberculated. 

 although faint and partially coalesced tubercles occur on the five 

 remaining costae. A number of examples of this species, in- 

 cluding the type, are preserved in the Museum of Comparative 

 Zoology at Cambridge, Mass. 



Formation and locality. State Quarry beds (Upper De- 

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



Dipterus mordax Eastman. 



(Plate II, Figs. 4, 5; Plate VII, Figs. 5-9) 



1900. Dipterus mordax C. R. Eastman, Journ. Geol. 8, p. 39, text-figs. 6, 8. 

 1907. Dipterus mordax C. R. Eastman, Mem. N. Y. State Mus. 10, p. 161, pi. 

 4, figs. 5, 6. 



Lower dental plates attaining a length of over 3 cm, coronal 

 surface gently convex, with six rows of very large, discrete, 

 conical or rounded tubercles which extend from the outer mar- 



