66 UNIVERSITY OF MISSOURI BULLETIN 



Formation and locality: Upper Devonian, Louisiana, 

 Mo., and Johnson County, Iowa. Collection of Mr. Rowley. 



ELASMOBRANCHI 



Some of the earliest of the pavement toothed sharks ap- 

 pear in the shales near Louisiana and are represented by six 

 species. Most of the teeth are small, but one is unusually 

 large for an Helodus. In the Chouteau at Sedalia, Missouri, 

 Helodus teeth only slightly different from those of the Devo- 

 nian occur. The Devonian teeth are simple and without 

 crenulations or surface markings, but the Chouteau teeth 

 have inconspicuous surface markings on most of them. The 

 Chouteau specimens show the beginning of the union of the 

 helodont forms to form the large cochliodont teeth that soon 

 after became abundant. Mr. Rowley has only ten of the 

 elasmobranch teeth in his collection and their rarity in the 

 Devonian may be judged from this. 



Helodus rowleyi sp. nov. 

 (Plate IV, figs. 25 and 26) 



This species is present above the usual fish bearing horizon 

 at Louisiana. The tooth is 48 mm. long and 21 mm. wide. 

 The root is 12 mm. high and 16 mm. wide and projects back- 

 ward. The vertical front edge of the crown is crenulate to 

 near the summit and the sloping, back margin is crenulate to 

 near the middle of the tooth. A low, broad, rounded boss 

 projects slightly upward a little to one side of the middle. 

 The specimen does not closely resemble any other described 

 Helodus. 



Collection of Mr. Rowley. 



Helodus devonicus sp. nov. 

 (Plate IV, figs. 19, 20) 



Type a single specimen in the collection of Mr. R. R. Row- 

 ley. Length of tooth 18 mm., breadth at widest part 6 mm., 



