DESCRIPTION OF SHELLS. 163 
ARTICULATA. 
ANNELIDA. 
Serpula ornata. (Tab. IX. fig. 21.) 
Spec. Cuar.—Partly free, tortuose, slowly increasing, surface marked with 
many slightly elevated thread-like ridges, the alternate ones more prominent ; 
ridges crossed by numerous, transverse, sharp, less prominent elevations or plates 
of growth; aperture circular ; apex spiral ? 
This has very much the appearance of a Vermilia, but the specimens are not 
sufficient to satisfy us that it is one. 
From the Collection of Mr. F. E. Edwards. 
MOLLUSCA. 
The chemical composition of the hard parts or skeletons of fossil Mollusca is 
the same as in recent, being of lime and carbonic acid, called carbonate of lime, 
similar to chalk. In America much of the mortar used for buiiding is made 
from burnt shells ; and in England, particularly in the crag districts, shells form 
a good manure. Molluscous animals have the power of increasing their habita- 
tions as their bodies enlarge, first, by successive additions of membrane to the sur- 
face, and secondly, by the hardening of that membrane by earthy matter secreted 
from their food. Nature, in the coverings of this extensive class of beings, 
seems to have no end of variety: yet how wonderful it is that these apparently 
insignificant creatures, working in silence and unseen, construct their shells on 
the most mathematical principles, and in the best manner suited for their peculiar 
wants: they have also the power of repairing fractures, and extending certain 
portions of their shell to secure their attachments to objects within their reach. 
It may be truly said from this adaptation, and the great beauty and variety of 
colour which many of them possess, that no work of man’s hands, no temple of 
Solomon can compare with the pearly lustre of their habitations *. 
* “We here find that a principle, which has only of late years been recognised and applied to the 
building of ships, namely, the diagonal arrangement of the frame-work, and the oblique position of 
the timbers, is identical with that which from the beginning of creation has been acted upon by 
nature in the construction of shells.” —Dr. Roget's Bridgewater Treatise, vol. i. p. 234. 
