FOSSILS THEIR NATURE AND INTERPRETATION. IOI 



Sertularidae) are also abundant in a few zones in the Paleo- 

 zoic rocks. Figures 12, 13, 14. 



FIG. 13. 



FlG. 13. Graptolite. Diplograptus palmeus Barr. Silurian. (S. and D.) 



FlG. 14. Coral. Parasmilia centralis Mant. sp. Cretaceous A, corallite, longitudinally 

 sectioned ; 2>, the same seen from above ; s and 1-5 = septa, c = columella. 



Echinodermata were represented in fossil form, developing 

 some hard parts in each order, viz. : Crinoidea, Blastoidea, 

 Cystidea, Ophiuroidea, Asteroidea, Echinoidea, and even the 

 Holothurioidea probably recognized in the spiculae. The 

 Solecida (parasitic worms, whether grouped with the Echino- 

 dermata, or with annelids under Vermes) are all soft, and do 

 not come within the province of the paleontologist. Figures 

 15-19. 



Vermes. Among the Vermes (the leeches, earthworms, 

 and sea-worms) there are some which produce earthy cases 

 of mud, others have left their tracks where they bored 

 through the tenacious mud ; also teeth have been found, sup- 

 posed to belong to thrs group. (See Serpula, Spirorbis, etc.) 

 Still, these are rare fossils, and probably represent but very 

 imperfectly the worms living in ancient seas. Figure 20. 



Arthropoda. Of the Arthropoda, including all those ani- 

 mals composed of definite segments arranged longitudinally, 

 one behind the other, and the locomotor appendages of which 

 are jointed or articulated to the body, we have four great 

 classes: Crustacea, Arachnida, Myriapoda, Insecta. All of 

 these produce a more or less enduring, horny or calcareous crust 

 or case, within which the soft parts are contained, making the 



