MECYNODON. 
35 
1867. Megalodon caeinatus, Quenstedt. Handb. Petref., ed. 2, p. 663, pi. Iv, 
fig. 27. 
1884. Mectnodon caeinatus, Tryon. Struct. Conch., vol. iii, p. 231, pi. cxxii, 
figs. 42, 43. 
1888. Megalodon caeinatus, Mheridge. Poss. Brit., vol. i, Pal., p. 161. 
1890. — ? PEOMiiSTENS, Whidhorne. Geol. Mag., dec. 3, vol. vi, p. 79. 
Description. — Left valve very inequilateral, long, rather narrow, transverse, 
convex. Umbo prominent, proximate, recurved spirally backward, situate at the 
extreme anterior point of the hinge-margin. Hinge-margin rather concave, about 
three-quarters the length of the shell. Anterior margin very convex, receding. 
Inferior margin nearly straight, slightly produced and concave at the postero- 
inferior point. Posterior margin slightly concave, very oblique. Back of 
shell divided by a very strong, elevated, angular ridge, rising at the back of 
the umbo, and arching round to the postero-inferior point in a sweeping curve, 
which is concave with regard to the postero-superior point, and does not 
apparently expand much beyond the rest of the shell. Contour, in front of this 
line of greatest elevation, at first concave, then oblique, and then curving in per- 
pendicularly to the margins ; and, in behind it, at first concave and then obliquely 
flat, till it reaches a much smaller angle or upward ridge, which arches concavely 
with regard to the hinge-margin from the umbo to the postero-superior point, and 
thus bounds a rather large, deep, lanceolate escutcheon. No lunule. 
Surface covered, in front of the first ridge, with rather numerous, irregular, 
distant, elevated, acute, transverse threads, separated by concave interspaces ; 
between the two ridges, with much more numerous close irregular threads or 
growth-lines ; and, on the escutcheon, with a few indistinct bulges. Shell-structure 
massive. 
Hinge with a long, large, linear, oblique, central tooth, next to which appears a 
ligamental gap, and at the posterior end a large, long, posterior tooth. Anterior 
lateral teeth unseen. 
Size. — Length 65 mm., breadth 33 mm., depth of single valve 20 mm. 
Locality. — There is a single specimen in the Museum of Practical Geology 
labelled " from Wolborough." 
Remarks. — I cauDot say that I am satisfied that the locality of this specimen 
is correctly given. The matrix is very different from that usual with Wolborough 
fossils. It is a soft yellowish-brown sub-oolitic rock, occasionally ferruginous. 
This seems to be slightly similar to the matrix of some of the Chudleigh fossils, 
but not to the generality of them. Is there any possibility of its being a Grerman 
fossil, which was placed by Mr. Godwin- Austen with his shells for reference ? 
It now appears to me that this fossil is most probably an aged specimen of the 
true Megalodon carinatus, Goldfuss ; for, although its shape does not quite agree 
