SPONGES OF BEAUFORT (N. C.) HARBOR AND VICINITY. 165 
Pleraplysilla latens n. sp. (Pl. LXIV, fig. 4o.) 
Sponge occurs in the shape of thin, colorless incrustations on oyster shells, commonly along with 
Microciona prolifera. Under the piers along the ‘‘town front’’ proved to be the best collecting ground. 
‘The sponge is not nearly so abundant as Microciona, but is not rare. It is, however, inconspicuous. 
It contains abundant embryos during July and August. 
Surface covered with small, sharp conuli, commonly o.5 to 1 millimeter apart. ‘Thickness of sponge 
from base to apex of conulus about 1 millimeter, usually something less; body of sponge itself about 
one-half that thickness. Upper ends of the skeletal fibers extending into conuli are conspicuous, reflect- 
ing the light. The fiber in some cases extends an appreciable distance beyond the substance of the 
conulus; but this may be an effect due to contraction. 
The dermal membrane in stained preparations exhibits narrow bands, which prove to be linear 
thickenings about 20 » wide, due to aggregations of mesenchyme cells on the under surface of the mem- 
brane. The mesenchyme cells are elongated in the direction of the bands. The bands radiate from 
the apices of the conuli, often about eight from a conulus, soon branching and passing into a network 
of similar bands which occupy the sides of, and the areas between, the conuli. The meshes of this net- 
work are polygonal, irregular in size, the diameter ranging from 70 4 to 250 u. The network is easily 
seen with a lens in a lightly stained preparation in alcohol. The bands are sometimes so arranged 
that primary meshes of the reticulum are subdivided. ‘The meshes themselves are riddled with small 
pores 12 to 24 4 in diameter. In the actual specimens examined the pores were open in some regions, 
closed in others. 
The dermal reticulum of bandlike thickenings just described is a structure similar to that found in 
Aplysina aerophoba, Aplysilla sulfurea, species of Spongelia, and other horny sponges (F. E. Schulze, 
1878, 1879a). It is of the same general character as that found in A plysilla longispina nobis (P1. LXV, 
fig. 48), but in the latter species the bands are relatively very thick and strongly developed, so much 
so that they constitute lateral walls of distinct, though short, canals, which may be said to traverse 
the dermal membrane radially. 
Beneath the dermal membrane there is a nearly continuous subdermal space from which canals, 
presumably afferent, pass vertically downward into the sponge interior. These canals are numerous, 
often about 0.5 millimeter apart, although there is no regularity in their distribution. ‘The mouths 
of the canals, reaching-about 300 » in diameter, are easily seen through the dermal membrane. With 
the lens they look like surface apertures and give to the sponge a porous appearance. 
Numerous tangential canals, presumably efferent, extend just below the dermal membrane. ‘These 
are long and branching, the larger about 0.5 millimeter wide. The membrane covering them is without 
conuli, and lacks or nearly lacks the system of bandlike dermal thickenings. It is in general aporous, 
but a few scattered pores occur of about the same size as those found elsewhere. Open oscula 2co to 
250 m in diameter were observed scattered over the surface of the sponge. 
The flagellated chambers are longer than wide, commonly ellipsoidal, often about roo to 120 by 
7oto gow. They may be larger, reaching 175 by 100 uw, sometimes slightly curved in the direction of 
the greater axis. Still longer tubular chambers occur here and there, sometimes with indications of 
branching. ‘These bespeak the primitive nature of the canal system. ‘The chambers are perforated 
by numerous prosopyles 8 to 10 » wide, and open by wide apopyles directly into the efferent spaces. 
The chambers are abundant below the general subdermal space, except in the regions of the main 
tangential canals, below which there are, however, some. 
The skeleton consists of simple independent fibers, 40 to 60 u thick at about the middle, ascending 
from the basal surface of the sponge into the conuli. They are made up of spongin and mineral particles, 
the latter including sand grains, fragments of sponge spicules, occasional entire spicules, and diatom 
shells. The mineral particles, except at the base of the fiber, nearly or completely fill it. Close to 
the base the mineral matter tapers away to a thin core, leaving the surrounding spongin very evident. 
In this region and at other points also along the course of the fiber it is possible to see that the spongin 
is laminated. At the very base the fiber expands into a thin basal plate of spongin. The fibers some- 
times extend vertically, or nearly so, from base to conulus. But usually they extend obliquely from the 
base upward, often occupying throughout a large part of their course a more or less horizontal position. 
They are sometimes fairly straight, but frequently curved or bent. They are characteristically simple, 
neither branching nor connecting. Rarely a fiber is found with a lateral branch; and, again, rarely 
two fibers may come in contact and fuse, thus producing the appearance of a fiber that divides basally. 
