371 
M. K. A. Zittel on Fossil Calcispongice. 
is a necessary consequence of the constitution of the calcareous 
fibres. Specimens with well-preserved, clearly-distinguishable 
spicules occur very rarely; much more frequently the minute 
skeletal elements are entirely or partially destroyed, and the 
fibres have acquired a structure which scarcely allows one to 
assume the former existence of spicules. 
It seems to me, therefore, that neither the size and the ex¬ 
ternal form, nor the constitution of the skeleton of the fossil 
fibrous sponges are opposed to their relationship to the Calci¬ 
spongice*. 
In the consideration of the fossil fibrous sponges their oc¬ 
currence in decidedly littoral deposits must also be of signifi¬ 
cance, as the existing Calcispongise, for the most part, live 
only at a very small depth. Most of them occur attached to 
stones in the littoral zone from high-water mark to a depth of 
2 fathoms. Very few of them go down to 20 fathoms ; but 
isolated forms have been brought up from 60-70 fathoms, and 
a single species (Leucaltis bathybia) even from a depth of 342 
fathoms according to Hackel. 
Although after the observations that have been made upon 
the metamorphosis of the fossil siliceous sponges into calcite, 
the chemical constitution of the skeleton can only be taken 
into consideration with great caution, it cannot be a matter of 
indifference that perhaps nine tenths of all the known fossil 
fibrous sponges, and these from the most diverse formations 
and localities, are in the calcareous state, and that silicified 
specimens usually occur only where nearly all the formerly 
calcareous shells and skeletons are converted into silica. 
Now that I have endeavoured to prove that the fossil 
fibrous sponges belong to the Calcispongise, it remains to 
discuss the further question, whether they enter one of the 
existing families or constitute an independent group. 
According to Hackel the Calcispongise are divided into 
three families—Ascones, Leucones, and Sycones. In the 
Ascones the thin wall is permeated only by transient cutane¬ 
ous pores or orificial canals; in the Leucones a rather com¬ 
plex system of branching canals is developed in the thick 
wall; and in the Sycones the whole sponge-body consists of 
simple radial tubes, which open into the stomachal cavity. 
The Sycones are represented in the fossil state by a single 
genus occurring in the Upper Jura. The calcareous fibrous 
sponges agree in respect of their canal-system neither with 
the Ascones nor with the Sycones; but there are among the 
• To my great satisfaction Mr. Carter, after I had sent him a number 
of fossil specimens, together with some microscopic preparations, has 
declared the existence of fossil Calcispongise to be indubitable. 
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