Grajotolites. 367 



posed it in 1858 for a repeatedly branching form, which I 

 detected in the shales of the south of Scotland. While the 

 paper in which I described this and other forms was passing 

 through the press, I learned that Greinitz had used the name, 

 but as I was unable to ascertain to what group he applied it, I 

 permitted the name to stand. In the same paper I described 

 a new species of Diclymograpsus. As I applied the name 

 obviously to a different group, it must, following the ordinary 

 rule in such cases, be retained for the forms to which I applied 

 it. This is a slender graptolite, looking like a pencil line 

 drawn in beautiful curves, or in nearly straight lines on the 

 surface of the laminas of the shale in which it is preserved. 

 The numerous branches are arranged sub- symmetrically on the 

 two sides of the primary point. 



Salter, in 1861, described a compound form from the 

 Skiddaw slates, similar to some that had already been observed 

 in Canada by Sir William Logan, to which he gave the name 

 of Dichograpsus. The fragments of this genus cannot be distin- 

 guished from imperfect specimens of the limited genus Grajp- 

 tolithus, but the discovery of the beautiful examples found 

 in Canada, and even of the less perfect ones obtained from 

 Cumberland, show that the complete organism was somewhat 

 complex. They were developed symmetrically from a primary 

 point, which Hall calls the "radicle," and dividing more or 

 less frequently in a dichotomous manner, they terminated in 

 greatly, apparently indefinitely, produced, simple, one-celled 

 branches. The slender bases of the branches at the centre of 

 the organism was supported by a flat, corneous disc. 



Hall, in 1857, established the genus Phyllograptus for a 

 remarkable form consisting of four series of cells, united to 

 each other by their longitudinal axes. In subsequently pub- 

 lished papers he proposed several additional genera for organ- 

 isms found in the Quebec rocks, some of which most probably 

 belong to other families than the graptolites. In some he 

 can detect no cell openings, and Inocaulis, which is not rare 

 in our British Silurians, has a solid homogeneous structure 

 very different from that of any graptolite. One of his new 

 genera is represented in Britain by two species, Dendrograptus, 

 a remarkable form in which a common stem to the polypary 

 is produced, apparently as in the recent Halecium, by the 

 aggregation of numerous tubes, which are the non-polypiferous 

 basal extremities of the branches. He has also established 

 two new genera for organisms that had found places in already 

 established genera. In Dijplograpsus the polypites were con- 

 tained in distinct hydrothecse (Plate II., Fig. 5) ; but in a few 

 species the cells bearing the polypites were excavated in the 

 margin of the common polypary (Plate II., Fig. 6), and for those 



