580 THE AMERICAN NATURALIST. [Vor. XXXIV. 
this highly fanciful sketch can be taken seriously, and, there- 
fore, the least said about it the better. 
Of the two leading theories as to the position in the body of 
Edestus “spines,” the first ascribes them to the jaws of a 
shark or skate, and the other to the median line of the back, 
some distance in advance of the dorsal fin or in a cephalic posi- 
tion. Dr. Bashford Dean! confidently asserts that the evidence 
of Edestus lecontet leaves no room to doubt that “the spine had 
its origin as a metameral structure whose basal portion lay 
within the integument, and traversed longitudinally a number 
(seven at least) of body segments." This supposed metameral 
origin of Edestus is still more strongly insisted on by the same 
author in his PzsAes, Living and Fossil (pp. 28-30). On the 
other hand, those who deny that these structures are dermal 
defenses and regard them as part of the dentition are impressed 
by the close similarity in form and structure of the enameled 
denticles as compared with ordinary sharks' teeth, especially 
those of Carcharodon and certain Palaozoic genera. As it is 
difficult to conceive of such unwieldy, bilaterally symmetrical 
bodies being located within the mouth cavity, they have been 
compared by the elder Agassiz with the rostrum of swordfishes, 
and by Miss Hitchcock with the symphysial dentition of Ony- 
chodus. Dr. Karpinsky’s conclusion that the spiral was exter- 
nal and attached to the upper jaw in the manner shown is 
based on the following considerations : (1) Helicoprion belongs 
undoubtedly to an elasmobranch ; (2) the bases of all the seg- 
ments (‘teeth ") of the spiral were imbedded in the soft parts 
of the fish; (3) the spiral must have been situated in the 
median vertical plane of the fish; (4) the whole of the spiral, 
except the large end, must have been exposed; and (5) the 
large size of the spiral (26 cm. in diameter) renders it highly 
improbable that it could have been contained within the mouth 
cavity. 
Dr. A. S. Woodward,? in a review of Karpiskys memoir, 
likewise admits that “the conception of a gigantic shark armed 
in both jaws with several series (whorls) of teeth, like those 
1 Trans. New York Acad. Sci., vag xv (1897), p. 68. 
? Geol. Mag., vol. vii (1900), p. 3 
