536 NEW YORK STATE MUSEUM 



loidea (with the exception of uubranched forms, as Azygograptus) crosses 

 over and places itself on the opposite side of the sicula. This often 

 prominent proximal part of the second theca, which in the multiramous 

 forms connects the common canals of the first four branches, has been termed 

 connecting canal by Holm, but this term was applied by Tornquist to the 

 first part of the first theca. Elles and Wood call it the " crossing canal." 



In the Dendroidea the branches consist of three different kinds of tubes : 

 large thecae, which are supposed to have contained nourishing individuals, 

 smaller tubes, which are budding individuals, and from which all three kinds 

 of tubes originate, and longer, narrow tubes (gonangia, after Holm and 

 Wiman; nematophores, according to Freeh). Fc^- further details see under 

 Dictyonema and Dendrograptus. 



In the Graptoloidea only thecae of one kind are observable Avhich 

 contained nourishing zooids. These exhibit in some compound Dichograp- 

 tidae (Groniograptus, Tetragraptus) certain differences proceeding from the 

 base of the colony in a distal direction, which are of an ontogenetic character 

 \_seech.7, p.531]. The apertures of the thecae are often provided with one or 

 several mucros or spines. These and other characters give to the theca a 

 bilateral symmetry. The external and internal apertures of the thecae are 

 in most or perhaps all Graptoloidea provided with a ringlike thickening 

 [see Perner, text fig.l, 2, and D i d y ni o g r a p t u s b i f i d n s , p.692, of this 

 publication]. 



In the axonolipous Graptoloidea the thecae grow in a distal direction 

 and are connected and held by their bases only, which form a continuous 

 canal (common canal). In the Axonophora the first theca assumes, after a 

 short distal growth, a reverse direction, ^v■hich is followed by all succeeding 

 thecae. These attach themselves to the nemacaulus. The latter is here 

 supported by an independently formed axis (virgula). 



It appeai-s that also in the heavier branches of the Axonolipa, as in 

 Tetragraptus amii [see pl.ll, fig.l] a support of the branches was 

 obtained by a thickening of the dorsal wall (common canal) of the branches. 



The hi'anching of the rhahdosomes takes place in different ways. In 



