Pleu. 700 



Plethomytilus knappi, Hall, Vol. 5, i. VIII c. 



Plethomytilns mytelimeris. {Lioceramus. Con.) VI. 



Pleuraoanihus arcuatus^ Newberry, Proc. Acad. Nat. Sci. 



Phil. Vol. 8. Coal 



measures. — Now Or- 



thacanthus arcua 



This -Rgii^ve will he fomid tus, Newberry, Pal. 



on page 506. Ohio, Vol. 1, page 



332, plate 40, fig. 4, 

 4 «, cross section. 

 Not uncommon in the 

 Cannel coal at Lin- 

 ton, O., bony spines, with traces of a medullary cavity, two- 

 thirds their length, but much smaller than the specimen de- 

 scribed by Agassiz, Poiss. Foss. Ill, pi. 45, figs. 8, 9, as 0, 

 cylindricus^ which was probably once curved like these, but 

 straightened by vertical pressure as some of the Ohio specimens 

 are. The toothing of the hind face of these spines is singularly 

 regular and beautiful ; the spines being coated with pyrites 

 look like metal stilletto blades. They probably belong to the 

 tish which left so many Diplodus teeth in the same coal mud. 

 See also what Newberry says on page 334. — Smaller, similar? 

 but straight spines are found in the same deposit and named 



by Newberry 

 Figure on page 506 above. Orthacanthus 



gracilis. Pal. 

 Ohio, Vol. 2, page 56, plate 49, fig. l.—XIII 



Note. — The genus was founded by Agassiz in 1843, Poiss. 

 Foss. Vol. 3, p. QQ, upon a spine supposed to belong to the order 

 Raiina^ serrated on one edge, curved at the base, and furrowed 

 at the lower side. The species named in this genus from 

 America are too poorly defined to warrant recognition. Type, 

 P. Icevissimus, (S. A. Miller, in his North American Geology 

 and Palaeontology, 1889.) He further quotes : — 



Pleuracanthus hiserialis^ Newberry, 1857, Proc. Acad. Nat. 

 Sci., Phila., Vol. VIII, p. 100. Coal measures. XIII 



Pleuracanthus dilatatu^., Newberry, 1867, Proc. Acad. Nat. 

 Sci., Phila., Vol. VIII, p. 100. Coal measures. XIII 



Pleuracanthus gaudryi, Brongniart. A restoration of the 



