DEVONIAN FISHES OF IOWA 141 



appressed in the fossil condition, although specimens that have 

 escaped deformation show that the cross-section is acutely tri- 

 angular along the line of insertion in the integument. 



The above definition has been emended and amplified in the 

 light of a fresh examination of Newberry's type material, and of 

 newly discovered specimens both of the present form and of the 

 closely allied Hamilton species known as Phlyctaenacanthus 

 telleri, in which the characters of the basal portion are well dis- 

 played. Heretofore doubt has prevailed as to whether the spines 

 referred to these provisional, and possibly identical genera, were 

 in reality segmented, this being a most unusual condition among 

 ichthyodorulites. This doubt is now dispelled. During the past 

 year an exceptionally perfect example of Phlyctaenacanthus has 

 been described and figured by Mr. Edgar E. Teller, of Milwau- 

 kee, which clearly demonstrates the dual' nature of the Hamil- 

 ton species named in his honor. A reference to his paper is 

 given below. Likewise, one of Newberry's originals of the Cor- 

 niferous form we are considering (that figured in Plate 31, fig. 

 5, of his Monograph of 1889), may be considered as proving 

 that the ''scutes", as Newberry calls them, of A. fragilis are 

 disposed in dual series, but not in groups of more than two, 

 as the original author imagined. 



The characters of the basal portion are well displayed in the 

 extremely small and no doubt immature spine shown in Plate 

 III, Pigs. 5 and 5a of the present contribution. The original is 

 from the "Corniferous" limestone of the Falls of the Ohio, and 

 is preserved in the Museum of Comparative Zoology. It shows, 

 as do also some undeformed specimens of Phlyctaenacanthus, 

 that the tenuous walls of the basal portions of both segments 

 were laterally expanded, and inserted in the soft parts in a man- 

 ner analogous to that seen in Stethacanthus. On decomposition 

 of the soft parts, the hollow cavity contained between the lateral 

 faces yielded to mechanical pressure, in the generality of cases 

 at least, thus bringing the walls of either side in contact, and 

 presenting a very deceptive appearance. This state of affairs 

 was remarked upon by Newberry, but somewhat differently in- 

 terpreted by him, in the following terms : 



