DEVONIAN FISHES OF IOWA 151 



portion laterally compressed, without trace of posterior denti- 

 cles, the sides traversed by about ten fine longitudinal costae. 

 The latter are non-bifurcating, regularly spaced, and of uniform 

 size with the exception of the large triangular one along the 

 anterior margin, which is twice the width of the others. 



Formation and locality. Chemung group; Delaware county, 

 New York. 



Genus homacanthus Agassiz. 



This genus, which strongly resembles Ctenacanthus, is thus 

 denned by Smith Woodward: "Dorsal fin-spines of small size, 

 slender, more or less arched, laterally compressed, and gradu- 

 ally tapering distally ; sides of exserted portion ornamented with 

 few, large, smooth, widely-spaced longitudinal ridges; a similar 

 ridge also forming a large anterior keel; posterior face with a 

 double series of large, downwardly curved denticles." 



American species that were formerly referred to Homacan- 

 thus, have, with but two exceptions, since been removed to other 

 genera; but at least one Devonian representative of this genus 

 seems to be indicated by the spines described in the following 

 paragraph. 



Homacanthus acinaciformis Eastman. 

 (Plate III, Fig. 10) 



1903. Homacanthus acinaciformis C. R. Eastman, Bull. Mus. Comp. Zool. 39, 



p. 218, pi. 5, fig. 58. 

 1907. Homacanthus acinaciformis C. R. Eastman, Mem. N. Y. State Mus. 10, 



p. 75, pi. 1, fig. 16. 



Spines comparatively small, slender, gradually tapering, gen- 

 tly and regularly arcuate ; lateral surface with five or six con- 

 tinuous longitudinal ridges; posterior denticles slender, rather 

 widely spaced. 



The small, gracefully curved spines referred to this species 

 are more strongly arched than those found in the Lower Car- 

 boniferous limestone of this country and Great Britain, but ac- 

 cording to J. W. Davis, much variation in curvature is to be 

 observed in spines belonging to a single species. Some resem- 

 blance is to be noted between the present form and the Upper 

 Devonian spines from Ohio described by Newberry under the 





