256 ROYAL SOCIETY OF CANADA 
Elasmobranchii hitherto determined, and is especially remarkable on 
account of the form of the root. There is much reason to believe that 
all the more primitive Elasmobranch teeth possess a horizontally ex- 
panded base (or root), while antero-posterior compression is the result 
of specialization. Such being the case, Protodus is a specialized form 
of a very simple type of tooth.’—Woodward, op. cit. 
(1) Proropus JExr, Woodward. 
Protodus Jeri, A. Smith Woodward. 1892. Op. cit. ante, p. 2, pl. 1, figs. 1 and la. 
“ Crown of tooth attaining a height of about 0.005, and measuring 
0.003 in width at the base; the apical half sharply bent inwards; 
coronal surface smooth, the lateral margins keeled, both faces convex, 
and the outer face with an unsymmetrically placed longitudinal ridge 
imparting to the tooth a twisted appearance. Root compact, stouter 
and much less deep than the crown.”—Woodward. 
Of this species there are five specimens in the Geological Depart- 
ment of the British Museum (Natural History), which were collected 
by Mr. Jex in 1891. 
(2) MESACANTHUS SEMISTRIATUS, Woodward. 
Acanthodes semistriatus, A. Smith Woodward. 1892. Geol. Mag. dec. 3, vol. ix, 
Do Dies des fetes 
This species is said to be “based upon a single imperfect fish,” 
in the British Museum (Nat. Hist.) collection, “ about 0.15 in length, 
and having the dorsal fin-spine 0.02 in length.” “Two large detached 
spines, however, Dr. Woodward adds, “ remarkably similar to those of 
the type specimen, may probably be regarded as indicating that the 
species sometimes attained to much larger dimensions.” “A. semi- 
striatus,” he remarks, “pertains to the primitive section of the genus 
(Mesacanthus of Traquair) already well known in the Lower Devonian, 
but attains to at least twice as large a size as any of its congeners 
hitherto discovered.” 
(3) CHEIRACANTHUS COSTELLATUS, Traquair. 
« 
? Cheiracan'hus costellatus.’ Traquair. 1898. Geol. Mag., dec. 3, vol. x, p. 46. 
“Several detached spines and one fish wanting the head,” are 
said, “to constitute the remains of this interesting species.” These 
were collected by Mr. Jex in 1892, and are now in the Edinburgh 
Museum. They have been thus described by Traquair. 
“The fish measures four inches in length, but it is so distorted 
and shortened up that its real dimensions and contour cannot be deter- 
