124 
On a Remarkable Pharetrond Sponge from Christmas Island. 
By R. KIRKPATRICK. 
(Communicated by 8. F. Harmer, F.R.S. Received August 16,—Read 
November 3, 1910.) 
(Printed by permission of the Trustees of the British Museum.) 
(PLATES 10 AnD 11.) 
The foundation of our knowledge of the Pharetron sponges was laid by 
Zittel in 1879 (9, p..11). He found, when classifying the fossil sponges, that 
after the Dictyonines, Lithistids, Tetractinellids, and Monaxonellids had been 
sorted out, there still remained numerous specimens, mainly calcareous, and 
ranging from the Devonian to the Cretaceous formations, in which the 
skeleton was formed of a network of anastomosing calcareous fibres with a 
very finely fibrous structure. 
In 1872 Haeckel (34, vol. 1, p. 8341) had declared that no fossil sponges 
belonging to the order of Calcisponges had been found, nor were ever likely 
to be, judging from the delicate texture of known Calcisponges. 
At first Zittel regarded the fossil “Calcispongia fibrosa” or “ Fibrous 
sponges ” as members of a wholly extinct order, in no way related to that of 
the true Calcispongie. Some regarded the fibrous sponges as fossil horny 
sponges, others as altered siliceous sponges, others again as corals. Zittel 
found, however, in the course of his investigations, that the fibrous markings 
in the fibres were due to the presence of uniaxial or three- or four-rayed 
spicules. This discovery led him to regard the fibrous sponges from a wholly 
new point of view, viz., as true Calcareous Sponges. | 
As the fossil Calcarea known at that time were, with one exception, 
apparently very different from the recent sponges belonging to Haeckel’s 
three families (Ascones, Sycones, Leucones), and as they seemed to be a more 
or less homogeneous group, Zittel included them in a new family, the 
Pharetrones.* His conclusions were at first disputed, and it was thought 
that the spicules composing the fibres were originally siliceous bodies, which 
had undergone calcification in the course of becoming fossilised. 
In 1882 Hinde (4, p. 185) described several very well preserved Pharetrones, 
in which not ‘only were the spicules visible in the fibres, but also separate 
three- and four-rayed spicules and “tuning-forks” could be distinguished in 
* gapérpa, a quiver, from the fancied resemblance of the Pharetron fibre to a quiverful 
of arrows. 
