GKAPTOLITBS OF NEW YOUK. I'AUT I 



503 



Fig.22 Dictyonema rarum Wiman. Frag- 

 ment of a branch etched out of flint. Shows tho 

 thecae and the apertures of the gonauKia. xll. 

 (Copy from Wiman j 



While our material, which is preserved in clay slates, seems unfit to 

 allow any such method of investigation as Wiman employed, it will at 

 least sometimes permit the observation of the composite nature of the 

 branches, as in the specimen reproduced in text figure 28. In this, some 

 parts have been slightly infiltrated with pyrite, which has brought out 

 plastically the narrow tubes, running alongside of the thecae and presum- 

 ably representing the " gonangia " and " budding individuals." The absence 

 of any axis is also distinctly shown 

 in this specimen. The numerous 

 large pores appearing on the sur- 

 face of certain compressed branches 

 are apparently the apertures of the 

 thecae. 



The question of the mode of life of the Dictyonemas has been mooted 

 repeatedly. Hall gave in Palaeontology of Ne%o YorTc, volume 2, plate 40, 

 figure 1, a figure [copied 1865, p.l2, fig.lO], which appears to indicate a 

 central root. This drawing has been cited frequently as proof that the 

 rhabdosome of Dictyonema was sessile. Hall, himself, does not mention 

 the presence of such a root in either the description of the species or the 

 definition of the genus. He states, on page 39 of the last mentioned work, 

 that " the Dictyonemas of the Niagara, Upper Helderberg and Hamilton 

 groups do occur in strata which contain large numbers of other fossils, 

 but we have no evidence of their having been attached. It is only from 

 their general form therefore and from their analogy with other bodies, 

 that we infer that these genera may have been attached to the sea 

 bottom or to some objects during their growth." Nicholson [1872, p.l2j 

 doubted the presence of the root; Brogger [1882, p.32] reports that he 

 found specimens of D. flabelliforme with siculae, the free end 

 of which is pointed, and that "that 

 attached, which in all probability may 

 general." 



species certainly was not 

 be right for the genus in 



