APPENDIX. 
539 
grasses, sea-weeds, and mosses. Walch, Wahlenberg, Schlotheim, and others 
referred them to Orthoceratites. Nilsson first considered them to be Polypes, 
and referred them to the family Oeratophyta, which included many forms that 
are now known to be widely removed from each other ; Beck and Barrande 
found their nearest allies in Pennatula, M'Coy in Sertularia, while Greene, 
Salter, and some others would raise them much higher in the scale and place 
them amongst the Molluscoid Polyzoa. To complete the history, we may only 
mention the absurd notion of Nimmo, that they are the serrated spines of Rays, 
of M'Crady, that they are the larvae of Echinoderms, and the equally absurd, 
although more elaborately defended, notion of Boeck, that they are torn frag- 
ments of animals of high organization. 
The Graptolite may be described as a Zoophyte with a free polypary, con- 
sisting of a flexible chitinous investment, surrounding the coenosarc and polype, 
or producing from its margin numerous cells which contained the polypes. The 
polype-cells were not cut off from the common ccenosarc by a septum. The 
polypary was strengthened by a slender solid axis, prolonged beyond the grow- 
ing-point. The structure agrees generally with that of the Sertulariadae ; but 
the solid axis is an anomaly, and to some extent also the free polypary. In some 
Actinozoa these two characters are found ; but in them the cells are hollowed 
out of the soft substance of the ccenosarc, and the free portion of the axis is at 
the proximal, and not at the distal end of the compound organism. The absence 
of any constriction or septum by which the individual polype was separated 
from the coenosarc distinguishes them from all the Polyzoa, the individuals of 
which are invariably seated on a septum. On the whole they approach nearer 
to the Hydrozoa, having the flexible external polypary and the common cceno- 
sarc continuous with the polypites j nevertheless they are an anomalous section 
of this group. 
Minute specimens of several species have been figured, differing from the adult 
forms only in their size and in the small number of their cells. No satisfac- 
tory evidence of anything like organs of reproduction has been observed in 
Britain ; but Hall has figured capsules attached to a double-celled Graptolite 
which he considers to be of this nature, and to have given origin directly to the 
minute forms which have been described. The only method of reproduction 
analogous to this among the Hydrozoa with which I am acquainted is in Tubu- 
laria, where the capsules give birth to progeny closely resembling the parents. 
The geological importance of Graptolites was first pointed out in the 1 Silurian 
System ; ' and nothing has since been discovered which has set aside the opinion 
then stated by Sir Roderick Murchison, that they were confined to and conse- 
quently characteristic of the Silurian rocks. 
The increased attention that has been given to this group of fossils, and the 
numerous forms that have been recently discovered, have required the establish- 
ment of several new genera. Professor James Hall has described a remarkable 
compound form, to which he refers all the species of single-celled Graptolites, 
believing that the forms previously described were merely imperfect fragments. 
However far this may be true of the American fossils, it is certain that many, if 
not all, of the European species of Graptolithus are perfect organisms, their 
primary point and their growing termination having been observed in several 
species. Salter therefore properly established the genus Dichograpsus for this 
compound form ; and the genera Cladograpsus and Cyrtograpsus contain other 
compound forms. Omitting those whose affinity to the Graptolites proper is yet, 
doubtful, the following are the genera that have been found in Britain : — 
2n2 
