624 J. W. DAVIS ON REMAINS OF FOSSIL FISHES 
peculiar form clearly separates it from any other species hitherto 
described. 
Genus Prevropvs, Agass.; Davis, Trans. Roy. Dubl. Soc. n. s. vol. i. 
p- 458 (1882). 
Prevropus Woopt, Davis, J. c. p. 458, pl. lix. figs. 12-15 (1882). 
(Plate X XVII. figs. 14-17.) 
In the British Islands the remains of this genus have previously 
been found only in the Coal-measures. The vertical distribution is now 
extended to the Yoredale beds or the upper beds of the Mountain- 
limestone series. The specimens found near Leyburn are considerably 
smaller than those of Pleurodus affins, Agass.*, from the Coal- 
measures. The latter are frequently three quarters of an inch in 
length and, compared with P. Woodz, are much longer in proportion 
to their width. The surface of the limestone species is evenly 
traversed by well-marked bilateral ridges extending from the central 
one towards each lateral extremity. In P. affims, the surface is 
often beautifully reticulated, and the connexion, if any, between the 
median ridge and the lateral projections of the margin is very slight. 
The arrangement of the teeth, and even the form of the body, of 
P. Rankinwi, Ag., have been indicated from fairly good specimensT 
by Messrs. Hancock and Atthey, and corroborative evidence given by 
myself with regard to P. affinis, Ag., from which it has been found that 
the body of the fish was very deep in proportion to the length, that a 
broad spine extended from the body in front of the dorsal fin, 
immediately behind the occipital region of the head, and that the 
body was covered with shagreen. The skeleton appears to have been 
entirely cartilaginous. The gape of the mouth was comparatively 
wide, and the teeth arranged in a single row on each ramus of the 
jaws, probably about twelve in number. 
The teeth now described are very rarely met with, only about half 
a dozen specimens having been discovered ; and hitherto no example 
of the spine of this genus has been found. 
Genus Prratopus, Owen, Odontography, p. 61; 
Davis, Trans. Roy. Dubl. Soc. n. s. vol. 1. p. 492. 
Prratopus acuminatus, Agass. (Plate XXVI. figs. 10, 10a.) 
Chomatodus acuminatus, Agass. Poiss. Foss. vol. iii. p. 108, pl. Lxix. 
figs. 11-13 (1833), and Poiss. Foss. vol. iii. pp. 174 and 384 (1840) ; 
Davis, J. c. p. 494, pl. lix. figs. 22-24. 
The specimens from the Yoredale Rocks of Leyburn differ in several 
important particulars from the type specimens described in the 
works cited above. The lower margin of the anterior surface of 
the crown is circular, and projects rather boldly forward ; the lateral 
* Quart. Journ. Geol. Soc. vol. xxxv. p. 181, plate x. figs. 1-11. 
+t See Hancock and Atthey, Nat. Hist. Trans. of Northumberland and Dur- 
ham, vol. iv. part ii. p. 408. And James W. Davis, Quart. Journ. Geol. Soc. 
1879, vol. xxxv. p. 181, pl. x. figs. I-11. 
