208 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Physonemus arcuatus M'Coy. 



(Text-figure 13.) 



1848. Physonemus arcuatus F. M'Coy, Ann. Mag. Nat. Hist. (2), Vol. II., p. 117. 

 1855. Physonemus arcuatus F. M'Coy, Brit. Palaeoz. Foss., p. 638, PI. III., Fig. 29. 

 1875. DrejHinacanthus revcrsus St. John and Worthen, Pal. Illinois, Vol. VI., p. 456, 

 PI. XIX., Fig. 5 (non Fig. 6). 



1883. Physonemus arcuatus J. W. Davis, 

 Trans. Roy. Dublin Soc. (2), Vol. I., 

 p. 367, PI. XL VII., Fig. 8. 

 1883. Physonemus falcatus St. John and 

 Worthen, Pal. Illinois, Vol. VII., 

 p. 252, PI. XXIV., Fig. 6. 

 1883. Drepanacanthus recersus St. John and 

 Worthen, Ihid., p. 253, PI. XXIV., 

 Fig. 5. 

 1899. Physonemus stellatus J. S. Newberry, 

 Monogr. U. S. Geol. Surv., Vol. 

 XVI., p. 200, PI. XXL, Fig. 12. 

 1902. Physonemus arcuatus C. II. Eastman, 

 Bull. Mus. Comp. Zo6\., Vol. 

 XXXIX., p. 87. 



All of the spines referable to this species 

 which have been previously figured are im- 

 perfect in this respect, that the superficial 

 ornamentation has been very largely de- 

 nuded, and the denticles along the concave 

 margin either worn or broken away, thus 

 obscuring their true relations. Although 

 the example shown in the adjoining Text- 

 figure has been somewhat injured, its gen- 

 eral outline is well displayed, and enough 

 of the ornamentation remains to leave no 

 doubt as to its identity with the type 

 species of this genus. The double row of 

 striated denticles bordering the concave 

 margin is fully as prominent as in typical 

 examples, although abrasion has reduced 

 many of the tubercles in size. One of the 

 latter ife represented seven times the natu- 

 ral size in the figure to the left of the spine. 

 Owing to the worn condition of the basal portion, it is not apparent to what 

 depth the spine was inserted in the integument, but from some other speci- 

 mens the writer has seen it is probable that it was not deeply implanted. There 



Fig. 12. 



Physonemus arcuatus M'Coy. St. 

 Louis limestone, Alton, 111. Lat- 

 eral aspect of spine, X x> ^"'^ 

 single denticle, X |. 



