BUITALO SOCIETY OF NATURAL SCIENCES 125 



be the front teeth of a Cochliodont shark, and it is a curious fact 

 that Jaekel^^" later proposed the same generic name for certain 

 Ptyctodont plates indistinguishable from those of Rhynchodus. 



It is obvious, from the new dental plates of Rhynchodus and of 

 Mylostoma described in this catalog, that the range of variation among 

 these forms has not hithferto been fully appreciated. These groups 

 apparently varied in many different directions, producing a bizarre 

 series of forms which we are only now first beginning to recognize. 

 Evidence is accumulating that the gap between the Rhynchodonts 

 and the Arthrodires will be bridged when these groups, particularly 

 the first, have become better known.^^ Even among the speci- 

 mens now in hand, there are a number that puzzle one as to 

 whether they should be referred to the Arthrodires or to the 

 Rhynchodonts. 



The following specimens are from the Onondaga limestone (Mid. 

 Devonic). All are from the Cement Quarry — excepting only E 1861, 

 which is from the Park Quarry — Buffalo, N. Y. Where not otherwise 

 indicated, they were collected by Mr. F. K. Mixer. 



E 2451 A spine-like element 72 mm. in length, and 18 mm. in 

 width at its wider end, tapering to a point. (PI. 42, fig. 

 I.) It is embedded in matrix but can be viewed from 

 three sides; of these the two lateral ones are covered with 

 tubercles, while the face between them is smooth. The 

 denticles are closely crowded, their bases touching, and 

 all point in the same direction, — toward the smooth face. 

 The latter consists of hard, smooth bone, and may have 

 functioned as a tritor. The opposite side, as shown by 

 other specimens, is excavated with roughened vascular 

 surfaces as though for a pulp cavity. 



E 1860 Dental plate. 



E 1861 Robust, conical, tuberculated, fragmentary tooth or spine. 



E 1862 Fragmentary, tuberculated plate. Collected by W. L. 

 Bryant. 



E 1863 Fragmentary tuberculated plate. 



^8* Jaekel, O.: Vehex Rhamphodus. Silzungsber. Ges. Nalur/orsch. Freunde, igos, -p. S92. 



*• Dollo, Louis.: Les ptyctodonts sont des arthrodires. Bull. Soc. Beige de Geol., xxi, 12 pp., pi. it. 



