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from their facility of recognition and from their very limited range 
in time. The genus Myophoria is confined to the Trias, and the 
two deep teeth at the hinge in either valve make it easily recog- 
nisable from the Trigonia, which has three teeth. The species Pes 
anseris is ribbed, so as exactly to resemble the foot of a goose. It 
does not last on into the Keuper ; it has just barely begun to ap- 
pear in the latest strata of the Muschelkalk ; it abounds in almost 
incredible numbers in the intermediate Lettenkohl. Now at Liine- 
burg, the limestone is almost made up of it alone, so abundant is 
it. This fact therefore connects these beds with the Lettenkohl. 
The Geratites nodosus confirms this conclusion. The entire genus 
is confined to the Trias.* It forms a link both in form and in 
time between the expiring goniatites and the yet future ammonites. 
The Geratites nodosus may be very easily recognised by the charac- 
teristic feature of the genus, which is, that in each septum all the 
lobes which point in towards the interior of the shell are toothed, 
while the projecting rounded saddle between each two lobes is 
smooth. The species nodosus is marked by thick ribs on the sides, 
radiating outwards, and terminating just at the edge of the back in 
high knobs or knots ; whence its name. The projection of these 
knobs being on the side of the shell, the back is rendered unusually 
broad, and has a very square appearance. Minute variations are 
very frequent, but are not sufficient to constitute more than mere 
varieties, and the general marks mentioned are unfailing. 
The Geratites nodosus^ then, thus easily recognised, is confined to 
the narrowest limits, as it first appears in the upper strata of the Mus- 
chelkalk, and disappears finally and for ever in the Lettenkohl, with- 
out so much as reaching the Keuper. Wherever found, therefore, 
it stamps the strata with one of the most definite assay-marks of 
science ; and such was the importance attached to its discovery in 
the Luneburg strata, that Von Strombeck, the great Triassic autho- 
rity of northern Germany, in the absence of the solitary specimen 
discovered, but unfortunately lost, refused to believe in its exist- 
ence. Since then, however, five other specimens have been found. 
They are mere casts, and but broken fragments of an inch or two 
^ It disappears wholly in the Jurassic, but reappears in a few species (four 
or five) in the Cretaceous. See Pictet, “ Paleontolgie,” vol. ii. p. 662. This 
is therefore an exception to the absoluteness of what is stated above. 
