158 CATALOG OF FOSSIL FISHES IN THE MUSEUM 



one margin. The bone itself of the element is also present (not as 

 in the three specimens mentioned above). The teeth are compressed 

 cones, higher than the width of the supporting element, pointed, and 

 compressed in the plane of the element. They bear a few stria- 

 tions in the basal half, somewhat like the teeth of Holoptychius; and 

 one tooth that is broken across shows that they have a large pulp 

 cavity. 



Taken all in all, the specimen suggests a mandible or other jaw 

 element with teeth, rather than a spine. But the element is narrower 

 in proportion to the height of the teeth than in any mandible known 

 to us. Perhaps it is comparable with such elements as Edestus, or 

 the intermandibular series of teeth and their supporting bone in 

 Onychodus. The present specimen seems to us to belong to a 

 Teleostome, rather than a shark; and may have held a median, inter- 

 mandibular position. This view finds some support in the fact that 

 the teeth are striated, reminding one of Crossopterygian teeth. We 

 propose the generic name Atopacanthus for this element (atopos, 

 strange, odd, eccentric; acantha, spine, thorn). 



The three elements referred to above as described by Hussakof in 

 1913 under the name Apateacanthus peculiaris, belong in the same 

 genus, and should henceforth be known as Atopacanthus peculiaris. 



Atopacanthus dentatus, n. gen., n. sp. 



(Text-fig. 54, A) 



E 2496 Type. — A fragmentary, narrow, compressed spine bearing 

 three large teeth along one margin. Length, as far as 

 preserved, 38 mm. (An additional 14 mm. is indicated 

 by impression in the matrix.) 



Formation and Locality. — Rhinestreet shale (Portage); forks of 

 Eighteen Mile Creek, near Hamburg, N. Y. Collected by W. L. 

 Bryant. 



Body of spine, slender, bearing along one margin large, conical, 

 compressed teeth, at right angles to the axis of the element. Unden- 

 ticled margin not perfectly straight but with a few very slight con- 

 vexities at short distances. Cross-section of element narrowly ellip- 

 tical. Teeth relatively large, increasing progressively in size in the 

 direction of the narrower end of the element; teeth with pulp cavity, 



