The specimens are all of the natural size except where the figures denote otherwise. (Original.)
1 and 2. Intestines of the two most common English species of Dog-Fishes, injected with Roman cement.
The vascular structure, which is still apparent in the desiccated membrane, resembles the impressions on the surface of many Coprolites.
3. Coprolite from the Lias at Lyme, exhibiting the spiral folding of the plate of digested bone, and impressions of the intestinal vessels and folds upon its surface. (See Note, V. I. p. 152. et seq.)
3'. Magnified scale of Pholidophorus limbatus, embedded in the surface of the Coprolite, Fig. 3. This scale is one of those that compose the lateral line, by which a tube passes to convey mucus, from the head, along the body of fishes; a. is the hook, on the superior margin, which is received by a depression on the inferior margin of the scale above it, corresponding with b.; c. is the serrated edge of the posterior margin, perforated at e. for the passage of the mucous duct; d. is a tube on the interior surface of the scale to carry and protect the mucous duct. (See note V. I. p. 150.)
3". Exterior of the scale 3'.; the same parts are represented by the same letters; the larger portion is covered with enamel; the smaller portion next d. is the bony root forming the anterior margin of the scale.
4. Transverse section of another Coprolite from Lyme, showing the internal foldings of the plate, with sections of scales of fishes embedded in it.
5. Exterior of a spiral Coprolite, from the Chalk Marl, near Lewes, showing folds and vascular impressions analogous to those in No. 3.
6. Longitudinal section of another Coprolite, from the same Chalk Marl, showing the spiral manner in which the plate was folded round itself.
7. Exterior of another spiral Coprolite, from the Chalk at Lewes, showing vascular impressions on its surface, and the transverse fracture of the spiral fold at b.
In many other figures of Plate 15, a similar abrupt termination of the coiled plate is visible at b.
8. 9. Two other small species of spiral Coprolites in chalk; these as well as Figs. 5, 6, 7, are probably derived from fishes found with them in the chalk, near Lewes.
10, 11, 12. Coprolites from the Lias at Lyme, exhibiting well-defined characters of the spiral fold, with vascular impressions on their surface.
13. Similar appearances on a Coprolite found by Dr. Morton in the Greensand of Virginia.
14. Coprolite from the Lias at Lyme, bearing strong corrugations, the result of muscular pressure received from the intestines.
15. Transverse section, showing the abrupt termination of the folded plate in Fig. 14, and representing the flattened form of the spiral intestine.
16. Longitudinal section of the intestinal tube of a recent Shark, showing the spiral valve that winds round its interior, in the form of an Archimedes screw; a similar spiral disposition of the interior is found in intestines of Dog-Fishes, Figs. 1 and 2.
17. Coprolite from Lyme, containing large scales of Dapedium politum.
18. Coprolite from the Lias at Lyme, containing undigested bones of a small Ichthyosaurus.