142 IOWA GEOLOGICAL SURVEY 



"In some instances the plates [i. e., fin-spines] are triangular 

 in outline, and seem to have been thin cones of bone or enamel, 

 supported by cartilaginous centers. As the latter are decom- 

 posed, the sides, which were once widely separated, were 

 brought together or crushed in like broken shells." — (Palaeozoic 

 Fishes N. America, p. 35.) 



Acantholepis fragilis Newberry. 

 (Plate III, Figs. 5, 5a) 



1857. Oracanthus fragilis, granulatus, abbreviatus J. S. Newberry, Proc. Nat. 



Inst. n. s., 1, p. 126. 

 1875. Acantholepis pustulosus J. S. Newberry, Kept. Geol. Surv. Ohio, Palaeont. 



2, pt. 2, p. 38, pi. 56, figs. 1-6. 

 1889. Acantholepis pustulosus J. S. Newberry, Monogr. U. S. Geol. Surv. 16, 



p. 34, pi. 31, fig. 5. 

 1889. Eczematolepis pustulosus S. A. Miller, North Amer. Geol. and Pal. p. 



586, text-fig. 1098. 

 1891. Acantholepis pustulosus A. S. Woodward, Cat. Foss. Fishes Brit. Mus. 



pt. 2, p. 129. 

 1907. Acantholepis fragilis C. R. Eastman, Mem. N. Y. State Mus. 10, p. 79, 



pi. 3, fig. 1. 



Major segment of detached fin-spines attaining a total length 

 of about 25 cm, and exhibiting the characters of the "genus". 

 Minor anterior segment spatulate in form, in general like that 

 of Phlyctaenacanthus, and with same tubercular ornamentation 

 as the principal spine. Arrangement of tubercles often varying 

 considerably, sometimes paralleling concentric growth-lines, and 

 generally finer and more closely crowded in small, immature 

 spines than in fully grown examples. 



The spines which are included under this provisional title,* 

 were first associated with Oracanthus by Newberry, but subse- 

 quently interpreted by him as dermal plates or scutes of "Placo- 

 derms", and supposed to be of similar nature as those which 

 have received the name of Acanthaspis. Subsequently their re- 

 semblance to the triangular ichthyodorulites of Psammosteus 

 was pointed out by Smith Woodward, before the true nature of 

 the latter genus had been ascertained. They are here interpreted 



*For the designation Acantholepis, preoccupied among insects, the late Mr. 

 S. A. Miller proposed the not too aesthetic sobriquet of "Eczematolepis", a pro- 

 cedure that proves the truth of Pope's lines: 



* * * Index-learning turns no student pale, 

 Yet holds the eel of science by the tail. 



