290 Graptolites. 



American species of Graptolithus are fragments of this more 

 complex form, I cannot say ; but it is certain that few, if any, 

 of our European species could belong to it. In many species, 

 the termination of both extremities of the polypary is known, 

 and that end by which they should be united to the compound 

 group is certainly free. Salter was right in considering this 

 compound form, as the type of a different genus, to which he 

 gave the name Bichograpsus. 



There is no indication in any of the forms of a hydrorhiza, 

 or of any means by which the polypary could have been 

 attached to a foreign body. In the branching forms a slender 

 initial process can generally be detected, to which Hall has 

 given the name "radicle/' but he does not consider this to 

 have been a means of attachment, and it is not possible that it 

 could have been so. We must consider that the graptolites 

 possessed free polyparies. 



Development. In 1858, I drew attention to young specimens 

 of B. tricornis, and published a drawing of one ; and in the 

 following year Hall figured the young of apparently the same 

 species. At the earliest stage these show all the characters of 

 the adult. There is the solid axis continued above the poly- 

 pary, and the three spines at the proximal end. Whether the 

 ct radical " in branching forms be the initial point in the develop- 

 ment, it is evident, that the axis exists in the earliest state of 

 Biplograpsus. At first a thin membrane is spread out between 

 the spines and the slender axis at the distal end (Fig. 10 d). 

 Next, there appear distinct indications -of the hydrothecae (Fig. 

 10 b and c) ; and these increase in number until the organism 

 attains considerable size (Fig. 10 a). I have traced the history 

 of B. pristis from a very young form like what has been by Mr. 

 Nicholson, in the current volume of the Geological Magazine. 

 At first they appear as triangular bodies, with the axis 

 developed at both extremities (Fig. 7 a and b) . The apex is 

 the proximal end, and at the base the cells are developed (Fig. 

 8 a and b). ' In Bidymograpsus I have observed specimens in 

 which Hall's "radicle/' with a single cell on either side has 

 formed the whole polypary. 



The origin of these minute forms has not been clearly 

 traced. Hall figures a species of Biplograpsus, bearing what 

 lie believes to be reproductive sacs. This figure is reproduced 

 on our plate (Fig. 8) . Nothing like this has yet been found in 

 Europe, but I have found several specimens of B. pristis, 

 showing a series of interlacing fibres rising from the hyclro- 

 thecse (Fig. 6), similar to what Hall figures as the marginal 

 fibre by which the reproductive sacs were attached to the axis 

 of the graptolite, but from which the sacs themselves had been 

 removed by maceration. He figures in connection with these 



