98 DR. J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Jan. 28, 
contraction. Their margins are entire, and their surfaces perfectly 
smooth and even. 
In a section made at right angles to the surface of the sponge, a 
portion of the expansile dermal tissue remained in situ, and the 
sharply conieal shafts of the connecting spicula were seen projecting 
into the space between the dermal membrane and the surface of the 
rigid skeleton of the sponge. The spaces of the rete of the skeleton 
are tolerably equable, but without any approximation to order in 
their arrangement. The fibres of the skeleton are cylindrical and 
quite smooth, excepting at their free terminations, which are fre- 
quently abundantly tuberculated. The tubercles are cylindrical, 
with hemispherical terminations, and are usually about once their 
own diameter in height. . 
The interstitial membranes are very pellucid, and-are rather abun- 
dantly supplied with the same description of tension-spicula that are 
so abundant in the dermal membrane ; and they may also frequently 
be seen imbedded in the sarcode that surrounds the skeleton-fibres. 
A few gemmules were observed ; they were globular, membranous, 
and very like those of Iphiteon panicea ; they were adherent to the 
inner surface of the dermal system. 
When sections of the sponge were examined in water, there were 
numerous moniliform series of spherical molecules, varying from 
three or four to six or eight in number, on the inner surfaces of the 
discoid heads of the connecting spicula, and also on the surfaces of 
the interstitial membranes. Such molecules in moniliform series are 
not uncommon in the sarcode of the interstitial membranes of many 
species of Halichondroid sponges; and this arrangement apparently 
arises from axial attraction. It is the first case of their occurrence 
that I have observed in the siliceo-fibrous sponges. 
DESCRIPTION OF THE PLATES. 
Puate IIT. 
Fig. 1. Surface of the rigid skeleton of the type specimen of Dactylocalyx pu- 
miceus, Stutchbury, exhibiting the irregularity of the skeleton-struc- 
ture and the auxiliary skeleton-fibres in the large interstitial cavities 
opposite, a, a, a, magnified 108 linear. 
Fig. 2. A rectangulated hexradiate tension-spiculum, magnified 108 linear. 
Fig. 3. A portion of one of the large fusiformi-acerate spicula from amidst 
the rigid skeleton of the type specimen of D. pwmiceus, magnified 108 
linear. 
Fig. 4. A trifureated spinulo-hexradiate stellate retentive spiculum, magnified 
666 linear. 
. A trifureated attenuato-hexradiate stellate retentive spiculum, magnified 
666 linear. 
Fig. 6. A large and a small yerticillately spined spiculum from the basal portion 
of the type specimen of D. pwmiceus in the British Museum, mag- 
nified 108 linear. 
Fig. 7. Subequiangular triradiate tension-spiculum from the type specimen, 
magnified 108 linear, 
Fig. 8. Acerate tension-spiculum from the type specimen, magnified 108 linear. 
Fig. 9. A furcated attenuato-patento-ternate connecting spiculum from the type 
specimen, magnified 108 linear. 
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