of the Genus Ptilograpsus in Britain. 239 
with specimens of a new species of Ptilograpsus, which I pur- 
pose to describe briefly under the name of P. anglicus. ‘The 
generic characters of Ptilograpsus consist in the possession of 
a branching plant-like frond, the branches and branchlets 
plumose. The pinnules spring alternately from opposite sides 
of both the primary and secondary divisions of the frond, and 
are celluliferous on one side only. The base of the frond is 
not known, the probability, however, being that the organism 
was fixed. 
As pointed out by Hall, Ptilograpsus closely resembles the 
modern Plumularia ; and,as far as its characters are yet known, 
there is perhaps no really important point of difference. Cer- 
tainly the resemblance to such forms as Plumularia cristata 
and P. myriophyllum, the first especially, is most striking, 
and must be more than merely mimetic. Like Dictyonema, 
Dendrograpsus, and Callograpsus (all genuine Graptolites), 
Ptilograpsus was probably permanently attached, though in 
none of these genera has the commencement of the “ hydro- 
eaulus”’ been yet detected. Another point in which Pelo- 
grapsus agrees with the above-mentioned genera and differs 
from the great majority of Graptolites is in the apparent ab- 
sence of the “ solid axis’’*, the individual branchlets consisting 
simply of cellules or ‘‘ hydrothece ” springing from a common 
canal or “‘ccenosarc.” By this absence of the solid axis, of 
all Graptolitic structures the most anomalous, Péilograpsus 
manifestly approaches very closely to the Sertularian type, 
though not more closely, perhaps, than do Callograpsus and 
Dendrograpsus. Dictyonema, again, though certainly belong- 
ing to the same natural subgroup of the Graptolitide as the 
above three genera, has a fresh structure superadded in the 
shape of transverse dissepiments connecting together the dif- 
ferent branches which constitute the frond. 
Ptilograpsus anglicus, spec. nov. 
Spec. char. Frond slender and branching, all the branches, 
large and small, being provided with pinnula, which spring 
alternately from opposite sides, and bear angular cellules on 
one face. Pinnule from twenty to twenty-eight in an inch, 
their length varying from two to three twentieths of an inch. 
_ * The “solid axis” has usually been supposed to be an essential element 
in the structure of every Graptolite, the genus Retiolites alone excepted. 
In common with the great majority of writers on the subject, this belief 
was shared by myself, and I did not believe that even the above-mentioned 
exception would be found to hold good. Recent investigations, however, 
into this particular point have led me to the opinion that the axis is not 
so constantly present as has been generally thought, that it is certainly 
absent in the genera I have spoken of, and probably absent in others. 
