60 Dr. H. A. Nicholson on the Graptolitide. 
never be preserved in a fossil condition. With regard to 
Dendrograpsus (Pl. IIT. figs. 16, 17) and Callograpsus (two 
genera which more closely resemble the Sertularide than any 
other), the probabilities are, perhaps, in favour of their having 
been fixed, though there is no decided evidence in support of 
this view ; and the same may be said of Dictyonema. 
Allied forms.—The affinities of Giraptolites as regards other 
extinct organisms are few and uncertain. ‘There exists, how- 
ever, one allied form (Pl. ILI. fig. 19), which I described last 
year from the Dumfriesshire Shales under the name of Cory- 
— noides calicularis. In this the polypidom is in the form of a 
simple elongated tube, without any central axis, furnished at | 
the base with two spines, and expanding distally into a toothed 
cup or “hydrotheca.” In general form Corynoides closely 
resembles some of the Corynide or Tubularide ; but the “ hy- 
drosoma has certainly been free, and was never fixed by a 
hydrorhiza.” Whether Corynotdes should be included amongst 
the Graptolitide, or should be regarded as the type of a new 
order, is doubtful; but it is certainly allied to the Chipeoliiaal 
and greatly strengthens the belief that the latter belong to the 
Hydrozoa. 
Conclusion.—I have now endeavoured to show that the 
position of the Graptolitide amongst the Hydrozoa is sup- 
ported by the phenomena observed in their morphology, deve- 
lopment, and reproduction, in their mode of existence, and by 
the determination of allied forms. As to their exact place, it 
is certain that they cannot be referred to any existing order 
or even subclass of the Hydrozoa, and it is probable that they 
stand in the same relation to the recent Hydrozoa that the 
Trilebites do to the Crustacea. In the arrangement of their 
parts and in their mode of growth, as well as in the nature of 
their structural elements, they more or less resemble the 
Hydroid polypes; but they are widely separated by their free 
hydrosoma. On the other hand, they approximate to the 
oceanic Hydrozoa in the fact that they were free-floating 
organisms, and in the possession, by some forms, of an organ 
resembling a “ float.” In the present state of our knowledge 
it seems, therefore, most advisable that the Graptolitide should 
be held to constitute a new subclass, which will hold an inter-. 
mediate position between the fixed and oceanic Hydrozoa, and 
which might possibly, on the derivative theory of develop- 
ment, be considered the primitive stock from which the 
above existing sections of our living Hydrozoa have originally 
diverged. 
EXPLANATION OF PLATE III. 
Fig. 1. Graptolites sagittarius, Linn., nat, size: showing the radicle (a). 
