72 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
appreciated by most writers on Edestus, and is thus ably summarized 
by Karpinsky :* 
“ Als Endzahne, Scheitelzihne 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 Hd. leconter und H. davisit 
das Gipfelende und das Basalende zu unterscheiden. Allein an den erhaltenen 
Exemplaren zusammengewachsener Segmente von Hdestus minor, EL. heinricha, 
und EL. giganteus bleibt sich die Grosse der Zaihne beinahe gleich und als das 
Scheitelende (das dlteste) dieser ‘Ichthyodorulithen’ betrachtet man meist 
das rechte in Figure 3[=type of H. minor] und das linke in Figure 5 [=type of 
E. heinrichi]. Mit andern Worten, man nimmt an, die Basis (Wurzel) eines 
jeden Zahnes richte sich von diesen nach der Seite der grdssern Ziihne (Seg- 
mente) hin. Die Vergleichung mit den Spiralsegmenten von Helicoprion 
dagegen fiihrt uns zu dem entgegengesetzten Schlusse, dass die meisself6rmige 
Basis der Zihne nach der Seite des Scheitelendes des Organs gekehrt 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. Newberry’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 :? 
“ Hdestus davisit 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 H. davis 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 [2.¢., deep]. 
Certainly such a monster would seem very much out of place in the lagoons 
of the coal marshes. Again, EH. heinricht 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 by additions to the acute 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 Loe. cit., p. 449. 
2 Monogr. U. S. Geol. Surv., Vol. XVI. (1889), p. 222. 
