REPORT OP THE STATE PALEONTOLOGIST 1901 



579^ 



.J 



This process of dichotomous branching and of the develop- 

 ment of one of the resulting branches into a denticulate branch 

 is repeated with absolute regularity. The result is the forma- 

 tion of four zigzag-shaped principal stems, lying in the diagonals 

 of the rectangle, and of two alternating series of denticulate 

 branches on each of these stems. 



Fig. 10, 11 are reproductions of more advanced stages which 

 differ from the younger ones principally in the length attained 

 by the denticulate branches. Both specimens bear 24 such 



Fig. 10 Idem. Stage where dichotomous 

 Fig. 9 Idem. Hydrosome with complete number branching has ceased and all new thecae 

 of branches seen from thecal side. x2J^ arrange themselves serially. Nat. size 



branches, six on each stem and none of the many hydrosomes ob- 

 tained at the Deep kill have a greater number of branches than 

 six. As the ultimate branches of the stems are both denticulate, 

 dichotomous branching appears to have ceased, and 24 seems to 

 be the maximum number produced by these colonies. Dr Ami, 

 however, figures a very large specimen, which, when complete, 

 would have had about 80 branches. Specimens in the writer's 

 hands attain about three fourths of the size of that referred to, 

 without bearing more than 24 branches; also the smaller speci- 

 men figured by Dr Ami possesses a greater number of branches 

 than colonies of like size in the Deep kill collection. These facts 

 seem to indicate that the latter material contains a variety 

 which, in the process of reduction of the number of branches, 

 observable throughout the Dichograptidae, has advanced a de- 

 cided step beyond the original Goniograptus thureaui, 



