DEVONIAN FISHES OF IOWA 233 



Formation and' locality. State Quarry beds (Upper Devo- 

 nian) ; Johnson county, Iowa. Sweetland Creek beds (Upper 

 Devonian) ; Muscatine county, Iowa. The occurrence of fish- 

 remains at the latter locality is reported by Professor J. A. 

 Udden in volume IX, page 302, of the Iowa Survey Reports 

 (1898). 



Synthetodus calvini, sp. nov. 



(Plate II, fig. 19; Plate X; Plate XI pars; Plate XII) 



1907. Undescribed Dipnoan dental plate, C. R. Eastman, M^ern. N. Y. Mua. 

 10, p. 203, pi. 4, fig. 15. 



Dental pavement attaining a somewhat larger size than in 

 the preceding species, and differing in that the three constituent 

 pieces of upper and lower dental plates respectively are more 

 intimately fused and non-sulcate, or with only indistinct sulci. 

 The functional surface above and below is quite smooth, gently 

 arched in a transverse direction, but becoming more or less 

 tabular in the worn condition, and sometimes developing a low 

 rounded eminence in the median portion anteriorly. 



Under this species are included the larger, more squarish, 

 flattened and tabular dental pavements of the same general pat- 

 tern as in the type species, but whose tripartite division is ob- 

 scured, owing to the more complete fusion of the median azy- 

 gous and paired lateral elements, with consequent effacement of 

 sutural depressions. Well preserved specimens are of tolerably 

 uniform appearance, but amid the inexhaustible series of worn, 

 corroded and water-rolled fragments obtained at the State 

 Quarry fish-bed, the tabular plates display equal diversity with 

 the rest. Such close intergradations exist among them as to 

 render it impossible to recognize more than a single species 

 besides the type, although until one has examined them closely 

 and attempted to define their limits it is difficult to believe that 

 there are not several. The writer himself was of the latter 

 opinion when the remains were first brought to light by Profes- 

 sor Calvin and his students. The microscopic structure of the 

 two species of Synthetodus here recognized is identical in all 

 respects with that of Dipterus. 



