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Dr. I. A. Nicholson on the Graptolitide. iar) 
1X.—On the Nature and Zoological Position of the Graptoli- 
tide. By Henry ALLEYNE NICHOLSON, D.Se.,M.B.,F.G.S. 
[Plate IL] 
THE Graptolitide constitute a group of extinct organisms 
which may be considered characteristically Silurian, though 
one genus (Dictyonema) passes up as high as the Middle Old 
in America. Their zoological position has always been: 
a matter of doubt; and they have been referred by different 
paleontologists to the Cephalopoda, the Hydrozoa, the Actino- 
zoa, the Polyzoa, and recently to the Foraminifera. The first 
and last of these views require no further notice; but the re- 
maining three are still maintained by different competent autho- 
rities, and the question must be looked upon as still undecided. 
In the following brief description of the morphology, develop- 
ment, and reproduction of the Graptolitide I purpose to draw 
attention to the facts which appear to favour the view, origi- 
nally put forth by Prof. M‘Coy, that the group should be re- 
ferred to the Hydrozoa. ! 
Morphology.—aAs to the morphology of the Graptolitide, 
the simplest form of Graptolite 1s composed of three factors, 
structurally and developmentally distinct, but united into a 
single lear stipe. These three elements (PI. III. fig. 2) 
are known as the “ solid axis,” the ‘‘ common canal,” and the. 
“cellules;”” and when combined together the solid axis is 
found as a cylindrical filament, or laminar plate, having on 
one side of it the common canal, from which, as a common con- 
necting substance, arise the denticulated cellules. In this way 
are formed those simple forms of Graptolites (Pl. ILI. fig. 1) 
to which alone the genus G'raptolites or Graptolithus ought to 
be restricted; and by the combination of such in various dif- 
ferent modes are formed all the remaining generic types of the 
Graptolitide. The simple uniserrate Graptolites thus com- 
posed, such as G. Sedgwickii, G. sagittarius, &c., have cer- 
tainly no direct representatives amongst either the Hydrozoa 
or the Polyzoa; but the corneous nature of the entire polypary 
and the presence of a “common canal” would seem to refer 
them to the former, since the latter have, as a rule, a more or 
less calcareous test, and the individuals forming the compound 
organism are not united by any organized connecting substance. 
There is, besides, an obvious resemblance between the mono- 
rionidian stipes and the separate branchlets of some of the 
lumulariz, such as Plumularia pennatula and P. cristata ; 
whilst the diprionidian forms constituting the genus Dv- 
plograpsus have an equally obvious analogy to the ramuscles 
of some of the Slate such as Sertularia abietina and 
S. jilicula, 
