No. 403.] KARPINSKY’S GENUS HELICOPRION. 58 I 
now described under the name of Helicoprion, is, indeed, 
sufficiently startling.” Nevertheless this distinguished expert 
brings forward considerable evidence in favor of the view that 
Edestus and Helicoprion should be looked upon as Palzeozoic 
sharks * with sharp, piercing teeth, which were never shed, 
but became fused into whorls as the 
animal grew." The question, then, as 
to whether these objects are segmented 
spines or teeth would seem to remain 
as puzzling as ever, in spite of the 
abundance of new light thrown on 
their structure by Karpinsky's studies. 
Analogy alone is insufficient to settle 
the problem ; we must have the positive 
evidence that only fresh material can 
supply. Should several whorls, or 
“spines,” be discovered in natural as- 
sociation, that is, belonging to one 
individual, it would be a fatal argument 
against their being dermal defenses, 
and we should have to look upon them 
as actual, veritable teeth, as suspected 
by Woodward. 
As far as analogy goes, however, no 
one can deny that there are a number 
of points in common between the 
segments of Helicoprion and various Fic. 1.—Sandalodus larvissimus. 
forms of cochliodont and petalodont ^ i44 ow gives eiie 
dentition, where the earlier formed pn ed Iaa: 
teeth are permanently retained, and she 
there are all degrees of fusion and coiling. Karpinsky 
himself calls attention to certain points of similarity in 
the structure of Janassa, Glossodus, and Helodus, and since 
his memoir appeared an important paper on the dentition of 
the first-named genus has been published by Jaekel! which 
calls to mind more forcibly than ever the resemblance to a por- 
! Jaekel, O. Ueber die Organisation der Petalodonten, Zeitschr. d. d. geol. Ges., 
Bd. li (1899), pp. 258-298. Cf. Text-fig. 1, p. 265. 
