DEVONIAN FISHES OF IOWA 177 



obliquely placed mouth, but in higher fishes is closed or ends 

 blindly. 



Formation and locality. Upper division of the Middle De- 

 vonian; Pelm, near Berlingen, Eifel District, Rhenish Prussia. 

 Holotype preserved in Museum of Berlin University. 



Family MYLOSTOMATIDAE. 



Headshield and abdominal armoring constructed essentially 

 as in typical Coccosteids, but with dentition adapted to crush- 

 ing instead of cutting. Upper triturating dentition consisting 

 of two pairs of Ceratodont-like palato-pterygoid dental ele- 

 ments, with non-denticulate margins. Well-developed vomerine 

 teeth present in the earlier, but not yet observed in later forms. 



Genus DINOMYLOSTOMA Eastman. 



A genus transitional between Mylostoma and Dinichthyids, as 

 its name implies, and partaking of the Characters of both. Man- 

 dibles with slightly prehensile symphysial beak, and broad, flat- 

 tened, regularly excavated functional margin, showing marks 

 of contact with dental plates of the opposite jaw, the latter 

 essentially as in Mylostoma. Vomerine teeth subtrihedral, 

 slightly prehensile. 



Dinomylostonia beecheri Eastman. 



1906. Dinomylostonia beecheri C. R. Eastman, Amer. Jour. Sci. ser. 4, 21, p. 



83, text-fig. 2. 

 1906. Dinomylostonia beecheri C. R. Eastman, Bull. Mus. Comp. Zool. 50, p. 



23, pi. 1, figs. 4, 5; pi. 2, figs. 13, 14, 16, 17; pi. 4, 5. 



1906. Dinomylostonia beecheri L. Hussakof, Mem. Amer. Mus. Nat. Hist. 9, 



pp. 119, 123. 



1907. Dinomylostonia beecheri C. R. Eastman, Bull. Mus. Comp. Zool. 50, 



p. 226. 



1907. Dinomylostonia beecheri C. R. Eastman, Mem. N. Y. State Mus. 10, p. 



151, pi. 14, figs. 5, 6; pi. 15. 



1908. Dinomylostonia [beecheri] B. Dean, Science, n. s., 26, p. 50. 



The specific characters of this primitive form are included in 

 the foregoing generic diagnosis. It may be noted, however, 

 that its particularly distinctive feature consists in the acute ter- 

 mination of both mandibles and vomerine teeth in front, together 

 with the deeply concave or excavated functional margin of the 

 lower dental plates. The triturating surface of all the dental 

 elements is narrower than in Mylostoma, thus making some ap- 



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