Vol. IX, No. 1. ] Sponges of the Lake of Tiberias. 79 
[V.8.] 
in Potamolepis, are often stout, smooth amphistrongyles mixed 
with a much smaller number of relatively slender amphioxi, 
but the skeleton is remarkable for the fact that the spicule 
fibres are usually, despite its compactness, of a somewhat ill- 
defined nature, thus differing from those of Potamolepis. 
which are often of two kinds, any specimen of Corvospongilla 
can as a rule be readily distinguished from any specimen of 
Potamolepis by the fact that minute birotulate spicules can be 
found lying free in the parenchyma of the former. In some, if 
not in all, species, however, the number of these spicules present 
is variable; sometimes it is so small that they can only be dis- 
covered with difficulty. 
Genus URUGUAYA, Carter. 
(Plate v, fig. 4.) 
ae Ann. gs Nat. Hist. (5), vii, p. 100 (1881); Pina 
wbid., (6), ii ae Pha Wiegm. Arch. f. Nat 
gesch., Ixi (i). p. 130 (1 
Sponge of stony ee forming crusts or nee 
growths with more or less cylindrical vertical branc The 
external surface is covered by a thick, chitinous membrane in 
spaces occur, having the appearance of granules. The sub- 
dermal efferent grooves take the form of ramifying channels of 
- small calibre, but it is impossible to say, after examining dri 
ed 
specimens only, whether there is a true afferent subdermal 
vity. 
Skeleton forming a dense net-work of vertical and trans- 
verse fibres firmly welded together. The individual fibres are 
very stout and contain a large amount of chitinous material, 
but the sheath it forms is never so regular: as in Veluspa. 
The vertical fibres are not distinguished in any way from the 
horizontal fibres and do not project upwards on the surface of 
the pI 
pi -—In all known species the skeleton spicules are 
stout amphietrumarion, but free amphioxous macroscleres also 
some. There are no free microscleres. The micros- 
clere of the gemmule consists of a short, comparatively stout 
shaft bearing an undivided rotule at either end. The rotules 
are equal and have the form of concave saucers, the sigh 
being in the same direction in the two belonging to each 
spicule. 
Gemmules.—The gemmules, which are small, adhere to the 
base of the sponge, and are poorly provided with or altogether 
lacking in pneumatic coating. Apparently they have no 
foramina. 
