CHONETES. 
117 
In many specimens the spines can be se§n to originate near the inner 
margin of the area, or along the hinge-line, and can he traced in the 
substance of the shell in an oblique direction inwards, at first nearly 
parallel with the margins of the foramen; and it is only after becoming 
free, that they take a vertical or obliquely outward direction. 
The nature of these tubes penetrating the substance of the shell, has 
been pointed out by Count Yon Keyserling*, and shown in his illustra¬ 
tions of Chonetes comoides; but this function has been doubted by Prof. 
De Koninck, who regards their obliquely inward direction as a con¬ 
trary indication.f In many of our specimens, however, I am able to 
trace these tubes through the substance of the shell from the hinge- 
margin (their opening into the interior being a little within the 
margin), beginning near the triangular foramen, and penetrating the 
shell to the upper edge of the area in lines parallel to the sides of the 
foramen. Those nearest the centre are more closely arranged than those 
at a greater distance : the former appear on the exterior as minute pus¬ 
tules, sometimes very close to the apex of the shell; and in receding 
from the centre, they become more prominent, and attain the character 
of spines. In some examples, the obliquity of the tubes within the sub¬ 
stance of the shell is seen to become less and less on receding from the 
apex, and they are often curved outwards before reaching the surface ; 
but the connexion of these tubes with the spines is unmistakable. 
In numerous examples of the casts left by the destruction of the ven¬ 
tral valve, the form of the tubes is well preserved in the infiltrated 
matter; and in these casts we often find evidence of the tubes near the 
centre, where no spines are visible on the exterior surface of the shells 
of the species, as in Chonetes logani and C. scitula. 
* Geognostiche Beobachtungen auf einer Reise in das Petschora-land : By Count Alexander Von 
Keyserling, 1846. 
t “ These grooves do not appear to me to be produced by the cardinal tubes, as Mr. De Keyserlino 
thinks, because iri this case they should take an opposite direction : I am led to believe that they depend 
solely on the successive growth'of the shell.” Recherces sur les Animaux Fossiles, p. 190. 
