28 
KXPI-AN ATION OF PLATK 15. 
4. Transverse section of another Coprolite from Lyme, 
shewing the internal foldings of the plate, with sec- 
tions of scales of fishes embedded in it. 
5. Exterior of a spiral Coprolite, from the Chalk Marl, 
near Lewes, shewing folds and vascular impressions 
analogous to those in No. 3. 
fc). Longitudinal section of another Coprolite, from the 
same Chalk Marl, shewing the spiral manner in 
which the plate was folded round itself. 
7. Exterior of another spiral Coprolite, from the Chalk 
at Lewes, shewing vascular impi-essions on its sur- 
face, 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. Twoother small speciesof spiral Coprolitesin 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 vas- 
cular 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 cor- 
rugations, the result of muscular pressure received 
from the intestines. 
15. Transverse section, shewing 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, shewing the spiral valve that winds round 
its interior, in tlie form of an Archimedes screw ; a 
similar spiral disposition of the interior is found in 
intestines of Dog-Fishes, Figs. 1 and 2. 
