356 Dr. G. J. Hinde on a true Leuconid Calcisponge 
established by Haeckel has previously been known. So fragile 
and apparently unfitted to be preserved as fossils are the 
structures of recent Calcisponges, that Heeckel did not think 
entire forms would ever be found in the rocks, though possibly 
their microscopic detached spicules might be met with 
(Kalksch. Bd.1. p. 341). And yet, by some most favourable 
combination of circumstances, this remarkable fossil Calci- 
sponge, as fragile as any of its existing relatives, has been 
preserved since Liassic times. Since Heckel’s Monograph 
appeared in 1872 numerous fossil Calcisponges have been 
determined by v. Zittel and others ; but all of them, with the 
exception mentioned above, belong to the extinct family of 
the Pharetrones, characterized by having a skeleton of solid 
spicular fibres. This structural type of Calcisponge appears 
to have been singularly well adapted for fossilization, since 
sponges of this group are recorded from Devonian strata up- 
wards; but as regards some of the older forms, from the 
Devonian to the Triassic, further evidence of the nature of 
their fibrous skeletons is still required. The skeletal fibres in 
the Jurassic and Cretaceous Pharetrones, however, consist of 
spicules closely resembling those of existing Leucones and 
other recent Calcisponges, and on this ground vy. Dunikowski 
placed them as a mere subfamily of the Leucones (‘ Palzeon- 
tographica,’ Bd. xxix. (1883) p. 34 sep. Abdr.), and believed 
that the solid fibres were of secondary origin, produced by 
fossilization. ‘This view is clearly untenable, since the spicules 
in the solid fibres of the Pharetrones have oftentimes a very 
definite arrangement, quite impossible to have been produced 
by mechanical influences from the irregularly intermingled 
spicules of Leuconid sponges. We now know from this Lias 
fossil that sponges with true Leuconid structure date as far 
back in geological time as any Pharetrones with definitely 
ascertained spicular fibres ; and it is not improbable that both 
groups may have coexisted from the Paleozoic era. It is 
worthy of note that whilst the Leuconid type still flourishes 
and is world-wide in its distribution, the Pharetronid type 
seems to have wholly died out, the latest known * occurring 
in the Upper Chalk. 
Distribution. The fossils were obtained by Mr. E. A. Wal- 
ford, F.G.8.f, in a bed belonging to the Marlstone of the 
* An Australian Calcisponge, Leucetta clathrata, Carter (Ann. & Mag. 
Nat. Hist. ser.°5, vol. xi. (1883) p. 33), was originally described by Mr, 
H. J. Carter, F.R.S., as possessing solid spicular fibres; but he has since 
discovered that the fibres are really tubular (7, vol. xvii. (1836) p. 508). 
+ I wish to state that the keen observation of Mr. Walford has also 
brought to light numerous other small Calcisponges in the Inferior Oolite 
of Dorsetshire, which are now under examination. They aye all Phare- 
trones, and include many new species. 
