28 EXPLANATION OF PLATE 15. 



4. Transverse section of another Coprolite from Lyme, 



showing 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, 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 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. 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 vascu- 

 lar impressions on their surface. 



13. Similar appearances on a Coprolite found by Dr. Mor- 



ton 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, showing the abrupt termination of 



the folded plate in Fig. 14, and representing the flat- 

 tened 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. 



