No. 89.] 



57 



This one and the preceding species are remarkably slender, and although serra- 

 ted on one side only, present some marked peculiarities when compared with the 

 singly serrated forms with central discs and a bilateral arrangement of the branches, 

 as in G. logani, G.flexilis, and G. multifasciatus. 



I 



Fig. 6. — Geaptolitus gracilis. 



The specimens of this species, which have thus far come under observation, have 

 still some points relative to the mode of growth undecided. It may have grown, 

 in the young state, as shown in figures 1, 2, 3. If, however, the little transverse 

 bar at the base indicates the original existence of two similar stipes or main 

 branches in addition to those already known, the mode of growth may still have 

 been similar, but having four instead of two main branches or stipes. If spread 

 out, as the specimens usually are upon the surface, it may assume the form of the 

 accompanying diagram, fig. 7. 



Fig. r. 



It is still possible that it may have assumed another form in its original mode of 

 growth, and that these small bifurcate fronds are but the separated offshoots from 

 a rhizoma which extended along the muddy bottom of the sea, giving off at inter- 

 vals the ascending stipes in pairs, which in their progress became branched as be- 

 fore shown; and in this case, the little transverse bar in the bending of the frond 

 is a part of the broken rhizoma. 



[Senate, No. 89.] 8 



