148 CTENACANTHUS, A ‘SPINE OF HYBODUS. 
eimem zweiten Bruchstiicke wird Ruckenstachel doppelt so 
.’ An evidently a description of a portion close 
to the apex of the spin 
We have now learnt the appearances presented by the spines of - 
this genus, fypm two of the greatest authorities ; and the portions 
of the spmes of Hybodus that I possess, and from which I made 
sections, correspond to the above descriptions. 
I will now refer to the external characters of the spines of 
Ctenacanthus in my possession and quote the descriptions < 
others ; we shall then be in a better position to institute co: 
pari sons between Ctenacanthus and Hybodus. Let us aha 
, 
postérieur se SR se quelques petites épines. surface est 
ornée de striés longitudinales, _ rapprochées que celles des 
elé 
saillantes en forme de dents at alternent d’une série 4 l'autre, 
mais qui semblent contmuer a cause de leur obliquité.” In 
describi 0. 
f 
vers sa pointe seulement, on remarque quelques petites épines, 
ou plutot quelques rides ‘plus saillantes en forme de peigne sur 
sillon margina _ Sa coupe transversale est ovale, arron 
du cdété de la face postérieur du rayon et tranchante as 
antérieur. La ligne de démarcation entre la partie aitonde du 
ca * * ot sa base lisse * * est trés-oblique.” 
e descriptions of Ctenacanthus given by McCoy in om 
“British Paleozoic Fossils,’ and by Messrs. Newberry a 
Werthen in the “ Geolo ical Survey of Iilmois, U. 8.,” 
similar to the above, with the exception that the spines they 
her 
ention are © d finer. M‘Ooy, however, meme 
that “the fin-defences of this genus are confi e Devonian 
an sae ocks, where they seem to > ieee the genus 
d 
yc Trae Meso Zoic period.” 
b ! 
none so setigi the C. major figured z in his “ Poissons 
Fossiles,” tome 3, tab. 4 —s the Rage senaretror tlie small 
and thin like Hybodus iw Be i . 10, fig. 
above work. They are generally a little arched, but are in some 
cases perfectly straight ; in ethers the anterior border is curved 
while the posterior is straight, the apex being bent in some cases, 
and in others not. tt tt 7 NE and gradually ond 
¥ 
Acassiz first. He says:—‘“ Les or wrerriene ont d’immense — 
me ** Ta 
= 
