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Cincinnati Society of Natural History. 



Genus: HeteracanThus. Newberry. 



Synonymy : 



1889. — Heteraeanthus, J. S. Newberry: "The Paleozoic Fishes 

 of North America;" Monograph, U. S. Geological Survey, 

 Vol. XVI., p. 65 ; Plate XXL, Figs. 4, 4a, and 5. 



1892. — Gamphacanthus, S. A. Miller: "North American Geol- 

 ogy and Paleontology — First Appendix," p. 715. 



Emended description of the genus: Pectoral (?) spines, 

 robust, covered with highly polished enamel, divided by nar- 

 row furrows into flattened longitudinal ridges, some of which 

 have their edges more or less regularly denticulated ; pos- 

 terior side straight and, along the greater part of its length, 

 broadly gouged into a rough groove for the attachment of 

 muscles; anterior side transversely arched, the anterior 

 profile /-shaped, being slightly convex near the summit, and 

 strongly concave toward the base, which is considerably pro- 

 duced forward ; the lateral sides of the shaft sub-equally 

 convex, flattening toward the base; the basal portion almost 

 flat on one (the outer) face, decidedly concave on the other 

 (the inner) face; the ridges are most numerous on the basal 

 portion of the spine, but terminate in succession above, so 

 that few reach the conical-pointed summit. 



As pointed out by Newberry, the want of symmetry in 

 these spines shows that they have belonged to some paired 

 organs; no doubt pectoral fins. 



In our specimen, the concave right face of the basal por- 

 tion (see Fig. 5) indicates that it has had its place on the left 

 side of the body. 



The base is obliquely rounded below on the inner face; on 

 the outer face it is bounded by two straight lines meeting 

 below at an angle of about 65 ; but as this side has been 

 trimmed rather too closely, I am uncertain whether or not 

 the said straight lines represent the original outlines of the 

 specimen, though it seems probable that nothing but the very 

 edge of the specimen has been removed. The number of 

 ridges on the base is about eighteen to the half-inch, and 

 each ridge is about one and one-half times as wide as an 

 adjacent furrow ; while, two inches from the summit of the 

 shaft, there are only about six ridges to the half-inch, and 

 the average width of a ridge is here about five times as great 

 as that of an adjacent furrow. 



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