Il8 AN INTRODUCTION TO THE STUDY OF FOSSILS 



I. Sketch the fossil; if the entire colony is not preserved, 

 dot in its probable shape and size. 



2. Where upon the colony did 

 K the individual animals live ? 



3. What probable difference 

 between the habitat of the young 

 and of the adult ? Reasons. 



Sub-order b, Graptoloidea. — 

 Colony (rhabdosome) simple, 

 or if branched it is not tree-like. 

 Cups (hydrothecae) usually dis- 

 tinctly marked and projecting. 

 The Graptoloidea lived sus- 

 pended, floating. 



This sub-order embraces two 

 divisions : — 



(i) Axonolipa. Virgula ab- 

 ^'S--- u'^'^r f ''^T.'"^ ■'^''^f 'S'T sent. Representatives of this 



Lichwald, from the lowest Ordo- ... 



vician of New Brunswick, showing division were suspended from 

 cups (r) and roots (r ). Natural geaweeds. Named from the 



size. (After Matthew.) 



Greek axon, axis, -f- lipein, to 

 lack, referring to the absence of the virgula. 



Phyllograptus (Fig. 42). Ordovician. 



Colony consisting of four short, broad, leaf-like (whence the 

 name from Greek phyllon, leaf) branches grown together, each 

 pair back to back, in such a way as to form a cross in section. 

 Hydrothecae upon the outer edge of each branch. 



1. Sketch entire colony, labeling the cups. 



2. Make an ideal cross section through the colony. 



(2) Axonophora. Colony with a median axis, or strengthen- 

 ing rod of chitin, called the virgula, running its entire length. 



The division Axonolipa is replaced from the mid-Ordovician 

 onward by the Axonophora, i.e. those with an axis (virgula). 

 This axis of chitin is brittle, which probably accounts for the 



