DEVONIAN FISHES OF IOWA 219 



coarse tuberculation and small number of radiating costae, the 

 type is a persistent one, reappearing with slight modifications 

 in D. mordax of the Upper Devonian. In the same way, the 

 laterally ridged Upper Devonian species, hereinafter described 

 under the names of D. costatus and D. digitatus, are probably 

 to be regarded as the lineal descendants of D. calvini, which 

 occurs near the summit of the Cedar Valley limestone. 



The holotype of D. uddeni has a total length of 36 mm, is 

 subtriangular in form, moderately convex, and remarkable for 

 the paucity of its denticulated ridges. These are but four in 

 number, and radiate outwards from the postero-internal angle, 

 which is worn smooth by use. The anterior row of denticles, 

 and inner moiety of the remaining rows are also considerably 

 worn; but in the outer moiety of these rows the denticles are 

 acutely conical, of large size, and well separated. There is a 

 gradual increase in size of all the denticles from the inner mar- 

 gin outwards. The coronal surface is finely punctate. 



Formation and locality. Base of the Cedar Valley limestone ; 

 Buffalo, Scott county, Iowa. 



Dipterus calvini Eastman. 

 (Plate II, Fig. 1) 



1899. Dipterus calvini J. A. Udden, Ann. Rept. Iowa Geol. Surv. IX, p. 283, 



(name only). 



1900. Dipterus calvini C. R. Eastman, Journ. Geol. 8, p. 38, text-fig. 7. 

 1907. Dipterus calvini C. R. Eastman, Mem. N. Y. State Mus. 10, p. 160, pi. 



4, fig. 1. 



Lower dental plate elliptical in outline, and moderately convex 

 in an antero-posterior direction. Eight tuberculated ridges ex- 

 tend from the outer margin to about the middle of the plate, the 

 two anterior ones larger than the rest and elevated into a slight 

 fold. Coronal surface considerably worn in the holotype, and 

 external margin partially broken. Tubercles conical and well 

 separated, except those of the two anterior ridges, which are 

 coalesced and worn on their summits. Total length of plate 

 3 cm. 



This species, like the preceding, is founded upon a unique 

 dental plate from the Cedar Valley limestone of Iowa. It comes, 

 however, from a higher level, locally known as the "Euom- 



