1169 
some specimens this crust is only one or two millimeters thick and 
then the surface is generally smooth and even. In others it is thicker 
and provided with small tubercles, lobes or ridges. Such specimens 
form transitions to more massive ones, albeit that they often rather 
simulate a massive mass, in reality being but incrustations. In the 
former case they are described under the names Spongia (Hymeni- 
acidon) sanguinea and Stylinos brevicuspis. Specimens like Hymeni- 
acidon caruncula, consimilis, mammeata ete. form transitions to such 
as are known as Awrinella erista-galli, Suberites (Crambe) crambe 
and fruticosus. In the simplest condition, as thin crusts, the skeleton 
is formed of vertical bundles of styli, branched or not, terminating 
in fan-shaped tufts. These bundles are attached to the substratum 
by means of a thin layer of spongine, which forms conical 
elevations in ‘which the bundles are firmly fixed with their basal 
parts. If the erust becomes thicker, localised or in general, the 
bundles of course grow higher; neighbouring bundles may be united 
by spicules, with or without the aid of spongine. This gradually 
leads finally to a sort of network of bundles, united by a very 
variable amount of spongine. Between the vertical bundles loose 
spicules may be found, often in a horizontal position i.e. parallel to 
the substratum. Moreover some acanthostyli occasionally occur; 
their typical situation is erect on the substratam. And finally, 
likewise in very variable number, sigmata and isochelae may be 
found. 
Let us now return to the desmas. 
In six of the inerusting specimens [| found desmoids, viz. in 958, 
977, 1026, 1037, 1039 and 1130. However, these organisms are 
never found regularly dispersed through the sponge, but only in 
certain parts. More especially they oecur at localised places of the 
base of the sponge, immediately against the substratum or, if they 
are found higher up, they are more or less in contact with the erect 
bundles of styli. This situation suggests that they are organisms not 
belonging to the sponge itself. Supposing this to be the case, where 
do they come from and what can possibly be their true nature ? 
It is highly improbable that they belong to some Lithistid, simply 
because I found Lithistids only twice or thrice in the Bay of Naples. 
It is a fact well known to everyone who has examined microscopic 
sections of sponges that they frequently contain foreign objects. 
Leaving out of consideration the numerous commensals we find in 
sponges, we often find spicules of other Sponges, Radiolarians, Fora- 
minifera ete. entirely incorporated in the parenchyma. Thus I found 
in some sections of specimen 975 spicules which had a great 
