364 University Geological Survey of Kansas. 



smaller of these teeth are mere tubercles of bone. The pre- 

 maxillaries are small, triangular elements, Joosely united to the 

 maxilla. They bear both large and small teeth, of which the 

 large are sharply pointed, smooth, and have anterior and pos- 

 terior cutting edges. The predentary is paired, and bears both 

 large and small teeth. 



The fins of this genus were first described as the dorsal fin- 

 spines of a shark, Ptychodus, by Agassiz, 121 but were later recog- 

 nized by Cope 122 as belonging to a teleost, and described by him 

 as a new genus, Pelecopterus , indicating a new order, Actinochiri, 

 and family, Pelecopteridse . These fins seem to form powerful 

 spines, and are composed of slender, parallel rods of bone, 

 closely placed. The anterior border is usually undulated more 

 or less, and, in the smaller species, with tooth-like processes 

 which are often covered with a substance which closely resem- 

 bles enamel. Remains of this genus are found in the Fort 

 Benton, Niobrara and Fort Pierre groups in Kansas. 



There seems to be some doubt concerning the structure of the 

 lower jaw, as the two authors, Cope and Felix, who have writ- 

 ten upon the subject, seem to entertain somewhat different 

 opinions. Cope 123 says : "A remarkable feature of the genus 

 is displayed in the mandibles. Each of these is compound in 

 the region usually composed of the simple dentary bone. It 

 there consists of three parallel elements — an internal and an 

 external, embracing a median element. The inner bears a band 

 of teeth en brosse on its inner and superior aspects, and the ex- 

 ternal a few teeth of similar character on its superior edge. 

 The large, lancet-shaped teeth are borne by the middle element, 

 excepting some of the largest near the symphysis. Two of these 

 on the inner side of the ramus originate in the internal bone." 

 Concerning this point Felix 12i says : 



"Wenn wir auch den Unterkiefer, abgesehen von dem Articular 

 und Angular, aus vier Stucken gefunden haben, dem Prsedentale und 

 Dentale, sowie einem vorderen und einem hinteren Spleniale, so 

 konnen doch dies nicht die Elemente sein, welche Cope meint. 



121. Poiss. Foss., vol. Ill, pp. 56-59. 123. Bull. U. S. Geol. Surv. Terr., p. 821. 



122. Cret. Vert. West, pp. 244, A-F. 124. 1. c, 287. 



