280 DR. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Apr. 6, 
harities of the skeleton; and in these fortunately there are very 
sufficient distinctive characters to assist us in the description of the 
species. In some of the little patches of this parasitical sponge 
there are several layers of the skeleton-structure, while in other cases 
it spreads like a single network over the surface of the sponge upon 
which it is parasitical. 
There is no definite arrangement in the skeleton-rete, and the 
areas assume a great variety of forms. The skeleton-fibre is always 
more or less depressed ; and in some cases two or more fibres coalesce, 
forming small broad plates of siliceous structure in which two or 
three canals may be seen running in parallel lines. The fibres in 
their normal condition vary to a considerable extent in their diameter : 
the largest measured was =}, inch, whilst the smallest was =j55 inch 
m diameter; the average diameter of four measured was +34; inch. 
The central canals of the fibres also vary in their diameter; the 
largest was =;1, inch, and the smallest => inch in diameter. 
Their course through the fibres is not always continuous; and fre- 
quent cases occur in which they terminate abruptly before reaching 
the angle of the network towards which they are progressing. 
The specimen described is the only ‘one I have yet seen; but it is 
probable that it will be found parasitical on other species of siliceo- 
fibrous sponges beside Farrea gassiati. 
The locality is the same as that of F. gassioti, lat. 14° 8'N., 
long. 77° 38' W., in 800 to 1000 fathoms. 
EXPLANATION OF THE PLATES. 
Puare XXXIX. 
Fig. 1. Farrea gassioti, natural size. 
2. A small portion of the outer surface of the skeleton of F. gasstoti from 
the distal margin of the specimen represented by fig. 1, x36 linear. 
3. A small portion of the piece of the skeleton represented by fig. 2, ex- 
hibiting the mode of the canaliculation of the fibre of the skeleton, 
x 80 linear. 
4 & 5. Two specimens of Farrea pocillum, natural size- 
6. A portion of the skeleton of F’. pocillwm from the specimen represented by 
fig. 5, exhibiting the more or less irregular mode of its reticulation, 
36 linear. 
7. Asmall piece of the skeleton of the specimen represented by fig. 4, 
exhibiting the spination of the skeleton-fibres and the numerous rec- 
tangulated sexradiate defensive organs 7 sttu, X 80 linear. 
8. One of the rectangulated sexradiate defensive organs, exhibiting the 
mode of its spination, * 150 linear. 
Piate XL. 
Fig. I represents a specimen of Deanea virgultosa, natural size. 
2. A portion of the skeleton of the specimen represented by fig. 1, exhibit- 
ing the rotulate mode of arrangement of the skeleton-rete and the 
large central canals within the fibre, x 36 linear. 
3. Farrea fistulata, natural size. 
4. A small piece of the skeleton of the specimen represented by fig. 3, 
exhibiting the quadrangular form of the rete and their large central 
canals, X 36 linear. 
5. A portion of a specimen of Farvea levis, natural size. 
5. A fragment of the specimen represented by fig. 5, exhibiting the form of 
