56 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



has been patent to nearly all writers. Perhaps the most novel conjec- 

 ture as to their function is that I'ecently advanced by Karpinsky/ who, 

 as an alternative hypothesis to regarding them as caudal spines, refers 

 the thrice-coiled spiral of Helicoprion to the snout region, and supposes 

 it to have been a powerful weapon for attack and defence, each 

 individual possessing but a single organ of this kind {cf. text-figure 1). 

 The Russian Director's main reason for excluding these spirals from the 

 mouth cavity, namely on account of their large size (26 cm. in diameter), 

 is not, in the opinion of at least two of his critics, an insurmountable 

 objection, nor can any argument for an external position be based on the 

 presence of so-called " placoid scales " over and around the bases of the 



segments or teeth, when it is 

 evident from the author's 

 beautiful figures that he has 

 mistaken calcified cartilage 

 for shagreen granules. 



In the reviews which have 

 appeared of Dr. Karpinsky's 

 memoir,^ it is admitted that 

 much evidence has been 

 brought forward in favor of 

 the view that Edestus and 

 Helicoprion should be looked 

 upon as Palaeozoic sharks 

 with sharp piercing teeth, which were never shed, but became fused 

 into whorls as the animal grew. And quite recently it has been 

 claimed by the present writer ^ that positive proof of the odontological 

 nature of Edestus, Campyloprion, and Helicoprion is furnished by com- 

 parison with the dental armature of Campodus. According to this view, 

 the curved or coiled "spines" of Edestus and Helicoprion are not der- 

 mal defences at all, but veritable teeth corresponding to the symphysial 

 series of Protodus, Campodus, the existing Cestracion, Carcharias, 

 Chlamydoselache and other forms, only more modified with respect to 

 curvature. Initial stages in the coiling of symphysial or intermandibular 



1 Karpinsky, A., Ueber die Reste von Edestiden, iind die neue Gattung Heli- 

 coprion. Verhandl. k. russ. Mineral. Ges. St. Petersburg, Vol. XXXVI., p. 467, 

 1899. 



2 Woodward, A. S., Helicoprion, — Spine or Tooth? Geol. Mag. (4), Vol. VII., p. 

 33, 1900. — ^rts^mon, C. R., Karpinsky's Genus Helicoprion: a Review. Anier. 

 Nat., Vol. XXXIV., p. 579, 1900. 



8 Science, n. s.. Vol. XIV. (1901), p. 795. — Geol. Mag. (4), Vol. IX. (1902), p. 148. 



Fig. 1. 

 Karpinsky's conjectural restoration of HeU- 

 coprion liessonowi, from tlie Russian Permo- 

 Carboniferous (after Karpinsky). X iV 



