72 BRITISH FOSSIL SPONGES. 
these nodes are given off simple and furcate rays with expanded ends as in the 
spicules with single separate nodes. In the normal elementary spicules of this 
family no definite canals have been observed, and even in the spicules of the sole 
existing representative, Vetulina stalactites, Os. Schmidt, canals do not appear to 
be present; at all events they are not mentioned or figured by Sollas' in his recent 
paper on this species. In the twin spicules of Cylindrophyma, however, as first 
pointed out by Dr. Linck,’ there is a well-defined simple axial canal in the short 
axis connecting the two nodes of the spicule, and this canal can occasionally be 
traced into the central portion of one or other of the nodes, thus proving that the 
twin nodes and the connecting axis form a single elementary spicule. The canal, 
however, does not give out branches into the rays of either of the twin nodes. In 
many of the spicules of Cylindrophyma Steinmanni,’ Linck, there is a gradual 
diminution in the size of the nodes and the rays proceeding from them, which 
become also more spinous, and they then resemble spicules of the Rhizomorina 
family, and can scarcely be distinguished from those of Cnemidiastrum Hoheneggeri, 
for example (Fig. 4,¢). On the other hand, the rays given off from the nodes of 
Anomocladina spicules are very similar to the branches given off from the main 
axis of Megamorina spicules, and the principal differences in the spicules of these 
two families consist in the fact that the spicular rays or arms in this latter 
proceed irregularly from an elongated axis, whilst in the former they proceed 
from a central node. 
Professor Zittel* has lately defined the elementary spicule of the Anomocladina 
family as consisting of simple, straight, or curved rods more or less branched at 
both ends, and forming nodes by the union of the branched ends of proximate 
spicules. Judging, however, from the characters of the spicules of the existing 
Vetulina stalactites, O. Sch., in which the central node, and the rays proceeding 
from it, evidently form a single structure, as figured by O. Schmidt’ and by Sollas,° 
and from the further fact that in the fossil examples of Cylindrophyma, the spicules 
produced by the disintegration of the skeleton likewise consist of nodes or centra 
with radiating rays, the evidence seems to be strongly in favour of the theory that 
these bodies are really the elementary spicules, and not, as suggested by Professor 
Zittel, compound bodies formed by the union of several simple rod-like spicules. 
(d) Yetracladina. In this family the skeletal-spicules are four-rayed; the 
rays or arms diverging from a common, non-inflated centre, at an angle of 120° 
from each other; they are either smooth (Fig. 5, ¢), or covered with small tuber- 
cles (Fig. 5, e). Near their extremities the rays divide into two or more branches, 
1 « Proe. Royal Irish Academy,’ 2 ser., vol. iv, No. 4, p. 486. 
2 «Neues Jahrb., &c.,’ 1883, ii Band, ster Heft, p. 59. 
3 Thid. 4 «Neues Jahrb., &c.,’ 1884, Band 4, p. 75. 
5 «Die Spongien des Meerbusen von Mexico,’ p. 19, pl. ii, fig. 9. 
6 « Proc. Royal Irish Academy,’ 2 ser., vol. iv, p. 486, pl. iv. 
