220 Repobt of the State Geologist. 



duced at first eight branches, as in Dichograptus oetobrachiatus^ 

 Hall, sp., and then 16-32 stipes as in Loganograptus. In a form 

 from the Hudson Kiver group, Hall counted as many as 40 stipes 

 branching from a common funicle. 



In all species, except some of the four stiped ones, the bases of 

 the stipes were found to be united bj " a more or less expanded 

 disc or cup of the same substance as the body of the Graptolites.'^ 

 Hall called it the "" central disc."* It is described as a thick 

 corneous test, which, in the simpl-e forms, is quadrangular, nearly 

 square, with straight margins, sometimes extended along the 

 margins of the stipes, as if to give strength and support to the 

 bases of the stipes. In forms with eight branches. Hall found 

 an octangular central disc, and in higher forms it becomes a 

 round disc. This keen-eyed observer found also that the central 

 disc is composed of two laminae which, at least in the central 

 portion, are not conjoined ; the spaces between the two, he sup- 

 poses to have been filled by some soft portion of the animal body. 

 We may still add that Hall observed that the bifurcation always 

 takes place within the central disc ; that the disc is not uniform 

 in its proportions; that it dees not always appear to bear the 

 same proportions to the strength of the stipes; and that it is 

 often striated parallel to the margins, which are thinner, the sub- 

 stance attenuating from the center. This is about all that is 

 known of the central disc, for, since Hall, 40 years ago, was 

 able to make his observations on the Quebec Graptolites, and to 

 give us a picture of the perfect form of some of these tiny fossils, 

 only few species which show such a growth have been found, and 

 these did not furnish any new facts regarding the composition 

 of the frond. 



The genera which are known to have grown in compound 

 colonial stocks belong to the Monoprionidae with single rows of 

 thecae, except two, i. e., Phyllograptus tyjpus^ Hall, with four 

 united basal stipes, and Betiograptus eucharis. Hall, from Blue 

 Point Lake, St. John, in which the stipes are united by ''slender 

 basal extensions " without the presence of a central disc. The 

 occurrence of a compound frond in this abnormal genus" is 

 especially interesting. 



The genus Diplograptus^ however, has hitherto been regarded 

 as producing only simple stipes, because some species which are 



♦ It Is absent in seme of the sub-bifurcated forms "apparently by accident." 



