3o8 AN INTRODUCTION TO THE STUDY OF FOSSILS 



animal matter. It molts at least once during the summer, at 

 which time it is sold in the markets as a " soft-shelled crab." 

 When raised for commercial purposes it is usually kept floating 

 in a box until molting occurs. (6) Lobocarcinus (Eocene). 

 This has a broad carapace, arcuate and much lobed in front. 



1. What is the geologic range of the members of this sub-class ? 



2. Give a common example of the order Isopoda. Its habitat. 



3. In what orders and era are the ancestors of the decapods 

 to be sought ? 



4. Name four living and one fossil example of the decapod 

 crustaceans. 



5. How many eggs does a lobster lay at one time ? 



6. What is a "soft-shelled" crab? 



7. What part of a malocostracan is most apt to be preserved 

 in the fossil state ? Why ? 



Sub-class 7, Stomatopoda 



The thoracic legs bend forward tow^ards the mouth, whence 

 the name from Greek stoma, mouth, -f pous (pod), foot. Known 

 in the fossil state from the Pennsylvanian to the present. The 

 mantis shrimp, Squilla (Jurassic to present), ranges from Cape 

 Cod to Florida. 



CLASS B, ONYCHOPHORA 



This class includes the single genus Peripatus, mostly confined 

 to the Southern Hemisphere. It looks much like a caterpillar 

 and is a typical arthropod except in its excretory and nervous 

 systems, in which it approaches the Annulata and flat-worms. 

 Of this very primitive class no fossil representatives are yet 

 definitely known, though a form from the Middle Cambrian 

 Burgess shale of British Columbia resembles Peripatus rather 

 closely. 



Derivation of name. — Greek onyx, a claw, -1- pherein, to 

 bear, in reference to the pair of horny claws terminating each 

 foot. 



