DEVONIAN FISHES OF IOWA 127 



the following species, and the accompanying fin-spines of the 

 form known as Heteracanthus will be noticed under a separate 

 caption. 



Formation and locality. Cedar Valley limestone; Waverly 

 and Waterloo, Iowa. Hamilton limestone; Milwaukee, Wis- 

 consin. 



Rhynchodus major Eastman. 



(Plate III, Fig. 8) 



1898. Rhynchodus major C. R. Eastman, Amer. Nat. 32, p. 487, text-fig. 42. 

 1900. Rhynchodus emigratus F. von Huene, Neues Jahrb. fur Mineral. 1, p. 



65, text-fig. 2. 

 1900. Rhynchodus major C . R. Eastman, Centralbl. fur Mineral, p. 177. 

 1900. Rhynchodus major C. R. Eastman, Amer. Geol. 25. p. 392. 



1903. Ramphodus tetrodon O. Jaekel, Sitzungsber. Ges. naturforsch. Freunde, 



p. 392, text-fig. 1. 



1904. Rhynchodus major C. R. Eastman, Amer. Nat. 38, p. 296, text-fig. 1. 



1906. Rhamphodus tetrodon O . Jaekel, Sitzungsber. Ges. naturforsch. Freunde, 



pp. 75, 181, text-figs. 1, 3, 5. 

 190/". Rhamphodus tetrodon L. Dollo, Bull. Soc. Beige Geol. 21, p. 1, pi. 2. 



1907. Rhynchodus major C . R. Eastman, Mem. N. Y. State Mus. 10, p. 69. 



1907. Rhamphodus sp. O. Jaekel, Sitzungsber. Ges. naturf. Freunde, no. 



6, p. 8. 



1908. Rhamphodus sp. B. Dean, Science, n. s. 2 7, p. 204. 



A species somewhat exceeding in size both R. excavatus and 

 R. rostratus, and distinguished from them by slight differences 

 in contour, especially by the more strongly convex anterior mar- 

 gin of both upper and lower dental plates. Upper dental plate 

 of considerably less vertical height than the lower, with more 

 slender and acutely pointed symphysial beak, and more retreat- 

 ing anterior margin; the sectorial margin strongly excavated 

 immediately behind the anterior beak. 



Lower dental plate relatively deep, with prominent, slightly 

 prehensile symphysial beak, behind which the sectorial margin 

 is regularly but not very deeply concave. Anterior margin 

 boldly and uniformly convex, produced downward into a long, 

 backwardly curved spiniform process similar to that in some 

 species of Ptyctodus. External surface smooth, or with only 

 fine concentric markings due to increment in growth, or occa- 

 sionally faint rugae. 



