34 
DEVONIAN FAUNA. 
is disappointing* to find that after all there is great perplexity in deciding its 
specific position. This arises in part from its great variability, which is at once 
observable in our figures, and in part from its similarity to another equally 
variable shell. 
• It appears to me that the shell Mecynodon carinatus, Goldfuss, sp., as given by 
him and other foreign authors, differs from the present species in several respects, 
e. g. in the posterior concavity of the hinge-line, the greater elevation and posterior 
facing of the umbo, the different shape and direction of the teeth, the contour 
of the dorsal keel, and some other points. These distinctions exist still more 
markedly in the shell next to be described, which we take to be a very aged 
example of Goldfuss's shell. 
To perplex the question still further there are several specimens from Paffrath 
t in the British Museum which, although labelled in German handwriting aa M. 
carinatus, agree with the present rather than with Goldfuss's form. 
The true solution might of course be that both forms belong to one 
extremely variable species ; but I think that, as far as our present evidence goes, 
the presumption is strongly against this. For instance, we may observe that 
these differences, which are as evident in small specimens, become accentuated in 
very aged shells. This may be seen by comparing the figures given in our 
PI. II, figs. 14 and 15. 
It is possible that the smallest of the specimens figured by Goldfuss belonged 
not to his species, but to the present shell. 
Affinities. — The shell figured as Megalodon carinatus by Phillips^ is totally 
removed both from the present and from Goldfuss's form. 
Megalodon bipartitus, F. Romer^ is a species founded on the cast of a some- 
what similar shell, which seems to differ in being longer, narrow behind, and in 
having a much stronger and larger muscle-mark. 
2. Meotnodon oaeinatus, Goldfuss, sp. PI. II, figs. 15, 15 a, 15 b. 
1834-40. Megalodus caeinatus, Goldfuss (pars). Petref. Germ., vol, ii, p. 183, 
pi. cxxxii, figs. 9 a — c, e,/'(only). 
1848. Megalodon cakinattjs, Bronn. Handbuch, pt. 3, p. 709. 
1853. ■ — — Steininger. Geogn. Beschr. Eifel, p. 55. 
1854. — — Morris. Catal. Brit. Foss., p. 209. 
1857. MECyNODON" carinatus, Keferstein. Zeitseh. Deuts. Geol. Gresell., vol. ix, 
p. 158. 
1 1841, Phillips, ' Pal. Foss.,' p. 136, pi. Ix, figs. 60* a, b. 
2 1844, F. Eomer, ' Ehein. Uebergangggeb.,' p. 78, pi. ii, fig. 2. 
