THE LITERATURE OF EDESTUS. 
C. R. EASTMAN. 
Ir has happened not infrequently that discoveries of the most 
surprising nature in paleontology have been made almost simul- 
taneously in different parts of the world. Hardly has some 
form of animal life, previously unheard of and apparently unique, 
been brought to light, when identical or closely related types 
are reported from remote regions. Familiar coincidences of this 
nature are recalled by Pareiasaurus amongst reptiles, Helicoprion 
amongst fishes, and Daemonhelix amongst problematical fossils. 
Although our knowledge of Helicoprion is comparatively 
recent, a very considerable literature has suddenly sprung into 
being concerning it and related forms, of which the older-known 
Edestus and Campodus are the most instructive and important. 
The latter, in fact, provides the only satisfactory clue we possess 
regarding the anatomical and systematic position of the whole 
series of Edestus-like forms. 
Without entering into any general discussion, it may be said 
that the majority of writers concur in the opinion that the 
“spiral saw” of Helicoprion and the arched segments of Edes- 
tus represent stages of that peculiar modification amongst Pale- 
ozoic sharks whereby series of teeth become fused and inrolled 
without being shed. The most recent communication that has 
appeared on this subject strikes a slightly discordant note, in 
that the author, Mr. Edwin T. Newton, suggests that Helico- 
prion and Edestus may not be of the same general nature after 
all. Although admitting that the former may be very plausibly 
regarded “as the enrolled dentition at or near the symphysis of 
an Elasmobranch, possibly allied to Cestracionts," his interpre- 
tation of Edestus is that it is a segmented dermal defence, such 
as a dorsal fin-spine. 
1 Newton, E. T. On the Occurrence of Edestus in the Coal-Measures of 
Britain. Quart. Journ. Geol. Soc., vol. 60, 1904, PP- 1-8, pl. 1. 
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