DEVONIAN FISHES OF IOWA 139 



portion is somewhat produced anteriorly, but to a less extent 

 than in H. uddeni, and without forming a very conspicuous 

 "shoulder" or Physonemus-like projection in front. 



Bilaterally symmetrical as these dermal defenses undoubtedly 

 are, their position must have been in the median line of the 

 body, and not, as suggested by Newberry and others, along the 

 front margin of the pectoral fins. That they were borne by 

 Chimaeroids (Ptyctodonts) seems very probable from the fact 

 that they are a constant accompaniment of the dental plates of 

 Ptyctodus and Knynchodus in the Middle Devonian of Iowa and 

 Wisconsin. The longitudinal extension of the base is a feature 

 which suggests comparison with the supporting cartilage of the 

 dorsal fin-spines in all recent Chimaeroids, and even the tri- 

 angular cross-section agrees with modern Chimaeroid condi- 

 tions. Both Eohon and Jaekel have noted the accompaniment 

 of European Ptyctodont remains by detached fin-spines, but no 

 specimen has been described in which they are seen to be nat- 

 urally associated. 



The present form of ichthyodorulite is a characteristic Mid- 

 dle Devonian species, and rather widely distributed. Numerous 

 specimens have been obtained from the Cedar Valley limestone 

 of Waverly and Waterloo, Iowa, and from the Hamilton of 

 Milwaukee, Wisconsin. One very well preserved spine showing 

 the closely spaced and finely denticulated costae is to be seen 

 in the State Museum at Albany, having been derived from the 

 Hamilton of Canandaigua Lake; and another is said to have 

 come from the Naples shale of the western part of New York 

 State. 



Formation and locality. Hamilton; Milwaukee, Wisconsin, 

 and corresponding Cedar Valley limestone of Bremer county, 

 Iowa; also Hamilton and Naples shale (Portage) of New York 

 State. Doubtful indications also in State Quarry beds of John- 

 son county, Iowa. 



Heteracanthus uddeni Lindahl. 



1897. Heteracanthus uddeni J. Lindahl, Journ. Cincinnati Soc. Nat. Hist. 19, 



p. 95, pi. 6. 



1898. Heteracanthus uddeni C. R. Eastman, Amer. Nat. 32, p. 557. 



1899. Heteracanthus uddeni C. R. Eastman, Journ. Geol. 7. p. 282. 



1907. Heteracanthus uddeni C. R. Eastman, Mem. N. Y. State Mus. 10, p. 83. 



