318 PALAEONTOLOGY OF ILLINOIS. 



genus has been noticed from the Coal Measures, ( 0. Alleni, St. J. and W.,) 

 and this form may prove to belong to the present genus. 



In the dedication of this remarkable genus of Hybodonts to the mem- 

 ory of Professor Agassiz, we but poorly, however appropriately, express 

 our appreciation of the profound labors of the great naturalist in this 

 field, and the impetus his researches gave to the cultivation of fossil 

 ichthyology ; and, in no less degree, the affection of a pupil for his 

 lamented preceptor. 



There remaius to be noticed the following forms relating to the genus 

 above described, of which it is thought there have already been deter- 

 mined four distinct species. 



Agassizodus vaeiabilis, (K and W., sp.) 



PI. Vin, Fig. 1-22. 

 Lophodus variabilis. Uewberry and Worthen, 1870; HI. Eep., Vol. TV, p. 361. PI. 4, Fig. 4, 5. 11. 



The typical species upon which the genus was based, is that here 

 referred to, and which was described from fragments of two teeth, and 

 the nearly perfect specimen, fig. 11, PI. IV, of the fourth volume of this 

 Eeport. The two former specimens, figs. 4 and 5, respectively repre- 

 sent unequivocal examples of teeth from the median and probably one 

 of the anterior rows of the mandible of the same species as that to 

 which the great jaw specimens previously noticed belong; fig. 4 

 showing the median prominence of the crown of the new tooth, as indi- 

 cated by the uuabraded state of the triturating edge, and tig. 5 pre- 

 serving a fragment of the anterior extremity of a tooth probably refer- 

 able to one of the anterior rows of the right ramus, as indicated by the 

 direction of the oblique sfcriation of the inferior basal surface. The 

 tooth figured in PL IV, fig. 11, however, apparently presents the 

 anomalous condition of a perfectly symmetrical tooth, the center of 

 which is suddenly produced into a very strong, lofty, laterally com- 

 pressed cone, the apex rounded from front to back, the angles present- 

 ing a delicate cutting edge marked in the upper portions by the minute 

 decussations or downward carved carina? common to the other examples. 

 Towards the base in the antero-lateral portions of the cone, the crown 

 is continued in a pair of lateral crests of apparently the same symmet- 

 rical proportions, and which diverge forward and downward at an angle 

 of about 90°. Only about one-third of their extent is represented in the 

 figure cited, and which partake of the characteristic conformation of 

 the more regular formed teeth. The lateral arms equal, at least, in 

 length the entire elevation of the median cone, differing from the nor- 

 mal appearance of the teeth of the lateral rows only in their compara- 

 tively more slender proportions, being much compressed antero-posteri- 

 orly, and the apparent obliquity of the anterior butteresses to the 



