150 CATALOG OF POSSIL FISHES IN THE MUSEUM 



FamUy COCHLIODONTID^ 



Synthetodus calvini Eastman 



(PI. 55, figs. I, 2) 



Undescribed dipnoan dental plate — Eastman, N. Y. State Mus., Mem. x, 203 



pi. iv, fig. 15. 1907. 

 Synthetodus cahini Eastman, Iowa Geol. Surv., xviii, 233, pi. ii, fig. 19; pis. x, 



xi [in part], xii. 1908. 



This species is represented by a single dental plate from the Conodont 

 bed, measuring 46 by 37 mm. (PI. 55, figs. 1,2). It agrees well with 

 Eastman's figure of the type (Devonic Fishes of Iowa, PI. ii, fig. 19), 

 and more especially with his specimen figured in Plate xii, figure 15. 

 The latter figure, which represents a somewhat smaller specimen than 

 ours, might almost have been drawn from ours. 



The occurrence of this species in the Conodont bed, is of consider- 

 able interest, as it gives us a second species — the other being Ptyc- 

 todus calceolus — common to this formation and the State Quarry 

 Beds (Upper Devonic) of Iowa. 



As regards the nature of these synthetodont elements, which have 

 been described as two species — Synthetodus calvini with a single 

 boss, and S. trisulcatus with a tripartite division of the wearing surface 

 — we find ourselves unable to concur in the opinion of Eastman that 

 they represent dipnoans. That they are dental plates admits of no 

 doubt; but the dental plates of dipnoans, with their radiating ridges, 

 or rows of tubercles, are among the most distinctive objects known to 

 the ichthyologist; and the present elements are clearly not of that 

 type. They may rather be compared with certain shark dental 

 plates, such as those oi Helodus. Each element is a flattened plate 

 (PI. 55, fig. 2), from one face of which rises a boss or tubercle which 

 functioned in triturating, as shown by its wear. And the entire face 

 is covered with a shining enamel (a little worn down on the functional 

 portion), which is sprinkled with small punctse, such as are seen on the 

 pavement dental plates of various sharks, e. g., Helodus. The other 

 face (PL 55, fig. i) of the dental plate consists of bony tissue, rough- • 

 ened with small depressions and postules, and obviously was the side 

 that was set in cartilage, or other soft, nutrient tissue. 



Moreover, the elements of both Synthetodus calvini, with their 

 single, central boss, and of S. trisulcatus, with their tripartite tritor, 

 are bilaterally symmetrical, and there are no rights and lefts among 



