eee rrr” 
FROM THE YOREDALE SERIES. ° 617 
tion has shown, do not seem to have survived during the deposition 
of the Millstone Grit or the Coal-measures. 
Genus CLrapacantuus, Agassiz. 
Cladacanthus, Agassiz, Rech. sur les Poiss. Foss. vol. ii. p. 176 
(1833). 
Erismacanthus, McCoy, Ann. & Mag. Nat. Hist. 2nd ser. vol. ii. 
p-. 119 (1848). 
CraDacaNTHUS PARADOXUS, Agass.; Davis, Trans. Roy. Dubl. Soc. 
n.s. vol. i. p. 365 (1882). (Plate XXVI. figs. 1-5.) 
The examples of this species from the limestone near Leyburn 
are only about half the size of those from Armagh in the Enniskillen 
collection, but in other respects they correspond essentially with the 
description given of the species in the Trans. Roy. Dublin Society 
referred to above. 
Cladacanthus paradowus, Agass., which has hitherto been found 
only in the Armagh limestone, by its discovery in the Red Beds of 
Wensleydale, has an extended range in locality, and also, what is 
perhaps of greater importance, an extension in the vertical series of 
strata from the lower massive limestones to the uppermost beds of 
the Yoredale series of Phillips, representing a long period of time. 
So far as observation has been made, however, Cladacanthus appears 
to be confined to the Mountain-Limestone series, and does not seem 
to have survived the advent of the period during which the Mill- 
stone Grit was being deposited. 
In the description of this species by Prof. McCoy *, the posterior 
or shorter arm of the‘spine is stated to have a double row of pos- 
terior denticles. In examples from Leyburn, it is clearly demon- 
strated that there is only one row, which occupies a median position 
along the compressed posterior margin of the spine. ‘The denticles 
are large, compressed laterally, and their apices point towards the base 
of the spine. The opposite anterior margin is formed into a broad 
and thick keel, more prominent than in the specimens from Armagh. 
Messrs. St. John and Worthen describe a species very similar to, 
if not identical with, the one described above, as Hrismacanthus 
McCoyanus (Paleont. of Illinois, vol. vi. p. 461, pl. xxii. fig. 1-5). 
‘It is chiefly distinguished by the more restricted posterior exten- 
sion of the tuberculose surface, and the less numerous costz, which 
reach to an oblique line descending from the angle of divarication.” 
Genus PHysonrmus, Agass. 
Physonemus, Agassiz, Rech. sur les Poiss. Foss. vol. i. p. 176 
(1833); MeCoy, Brit. Paleeoz. Foss. p. 638 (1855). 
PuysonEMus HAMATUS, Agass.; Davis, J. c. p. 370, pl. xlvil. fig. 9 
(1882). (Plate X XVI. fig. 6.) 
Onchus hamatus, Agass. Rech. Poiss. Foss. vol. iii. p. 9, pl. 1. 
Spine marked by its acutely rounded curvature. Greatest breadth 
* Toe. cit. sub nomine Hrismacanthus Jonesit. 
