72 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



appreciated by most writers on Edestus, and is thus ably summarized 

 by Karpinsky : ^ 



" Als Endzahne, Scheitelzahne oder alteste Zahne (oder Segmente) fasst man 

 bei den Edestiden mit Recht die von relative geringster Grosse auf. So ist 

 es nicht schwer, bei den vorliegenden Resten von Ed. lecontei und H. davisii 

 das Gipfelende und das Basalende zu unterscheiden. Allein an den erhaltenen 

 Exemplaren zusammengewachsener Segmente von Edestus minor, E. heinrichi, 

 und E. giganteus bleibt sick die Grosse der Ziibne beinahe gleich und als das 

 Scheitelende (das alteste) dieser ' Ichthyodorulithen ' betrachtet man meist 

 das rechte in Figure 3 [=type of E. minor'] und das linke in Figure 5 [=type of 

 E, heinrichi]. Mit andern Worten, man nimmt an, die Basis (Wurzel) eines 

 jeden Zabnes richte sich von diesen nach der Seite der grossern Zahne (Seg- 

 mente) bin. Die Vergleichung mit den Spiralsegmenten von Helicoprion 

 dagegen fiihrt uns zu dem entgegengesetzten Scblusse, dass die meisselfdrniige 

 Basis der Zahne nach der Seite des Scheitelendes des Organs gekeh'rt sei." 



The above interpretation of the three species of Edestus just enu- 

 merated is open to criticism on the ground that it assumes the segments 

 are reflected in the reverse direction from that known to obtain in 

 Campodus, Campyloprion, and Helicoprion, all of which have their teeth 

 bent forward toward the base. About this there can be no question. A 

 consideration of Dr. Xewberry's views on the same subject of orientation 

 and mode of growth in Edestus may not be out of place in this connec- 

 tion, and we quote from his latest published opinion as follows : ^ 



" Edestus davisii is more like the intermandibular crest of Onychodus than 

 are the other species of the genus. It is much more curved, and the arch of 

 bone from which the denticles arise is laterally compressed or longitudinally 

 grooved. Taken by itself, it renders the suggestion of Miss Hitchcock quite 

 plausible. But it cannot be taken by itself ; for wherever that species goes, 

 E. minor, E. heinrichi and E. giganteus must follow ; and while we can 

 imagine a fish ten feet long with an arch of bone like E. davisii held between 

 the extremities of the mandibles, it requires a much greater stretch of the 

 imagination to conceive of a shark of such size that this relatively insignificant 

 organ was twenty inches long and seven or eight inches wide [i.e., deep]. 

 Certainly such a monster would seem very much out of place in the lagoons 

 of the coal marshes. Again, E. heinrichi is nearly straight, a foot long, 

 rounded and massive at one end, thin and acute at the other ; but the succes- 

 sion of denticles was hy additions to the aciite end, which must have been behind, 

 for if it was situated in the symphysis, the blunt, rounded end would have 

 formed the apex of the arch of the lower jaw ; a condition of things scarcely 

 comprehensible. If, now, we transfer this spine to the position of the post- 



1 Loc. cit., p. 449. 



2 Monogr. U. S. GeoL Surv., Vol. XVI. (1889), p. 222. 



