124 IOWA GEOLOGICAL SURVEY 



upper and lower dental plates, though the latter are as usual 

 somewhat deeper, and both terminate anteriorly in prominent 

 beaks. The latter character is probably a generic one, and is ob- 

 viously correlated with their adaptation "au regime conchi- 

 frage", as Dollo calls it, together with a prehensile habit of 

 plucking hard-shelled food from the bottom. An excavation is 

 noted just back of the beak in the upper dental plate where the 

 terminal point of the lower came in contact with it, thus proving 

 that the relations between the parts functioned in the same 

 manner as in Ptyctodus. 



Formation and locality. Columbus and Delaware (="Cornif- 

 erous") limestone; Ohio. 



Bhynchodus excavatus Newberry. 

 (Text-fig. 18) 



1877. Bhynchodus excavatus J. S. Newberry, Geol. Wisconsin, 2, p. 397. 



1878. Bhynchodus excavatus J. S. Newberry, Ann. N. Y. Acad. Sci. 1, p. 192. 

 1878. Bhynchodus occidentalis J. S. Newberry, Ann. N. Y. Acad. Sci. 1, p. 



192. 

 1889. Bhynchodus excavatus, Monogr. U. S. Geol. Surv. 16, p. 50, pi. 29, fig. 



1 . (The original of this figure is the type specimen of the so-called 



B. occidentalis.) 

 1898. Bhynchodus excavatus C. R. Eastman, Amer. Nat. 32, p. 486. 

 1907. Bhynchodus excavatus C. R. Eastman, Mem. N. Y. State Mus. 10, p. 



68. 



A comparison of the type specimen of the so-called R. occiden- 

 talis, shown in text-fig. 18, with an extensive series of dental 

 plates from the Hamilton of Wisconsin, agreeing with New- 

 berry's description of R. excavatus, leads to the conclusion that 

 the two forms are identical. Indeed, it appears almost certain 

 that their identity had suggested itself to Newberry, since he in- 

 advertently confused the types of the two species at the time of 

 preparing his Monograph on Palaeozoic Fishes of North America. 

 In point of fact, the original exemplar of R. excavatus has never 

 been figured, and its actual whereabouts are unknown. On the 

 other hand, the specimen serving for the original description 

 of Newberry's R. occidentalis is now preserved in the American 

 Museum of Natural History in New York. The writer is in- 

 debted to Dr. L. Hussakof, of that institution, for calling his 

 attention to the fact that this is the very specimen which New- 



