62 
SHELL GALLEKY. 
organ has arisen by a further modification of an avicnlarium, whereby 
the horny lid of the latter has become a long bristle. The bristles 
Fig. 10. 
Scrupocellaria reptans. A. Creeping over seaweed, natural size ; B. Front 
surface, magnified. 
a, branched spine covering front of membranous area ; 6, avicularium ; 
c, vibraculum. 
C. Back surface ; a, vibracular cell ; b, vibraculum. 
by their motion keep off intruders, and possibly act as scavengers by 
sweeping the surface of the cells. 
In Caberia ellisii the vibracular cells are very large. The 
vibracula, which are long and serrated, have been observed to move 
in unison like a double row of oars. 
Case 
A 1,2. 
Case A 1. 
Al. 
Section B. Flustrina. — In this group the colonies form leafy 
lamellae, crusts, etc., in which the individual cells are typically in 
the form of oblong boxes with their front walls wholly or 
partly membranous. Flustra foliaceah&s already been described. In 
Flustra caroasea the fronds are formed of only one layer of cells, and 
not of two layers back to back as in F.foliacea. The fine specimen 
of Flustra nooilis from S. Africa is so called from the large size of its 
long hexagonal cells which form a honeycomb pattern clearly visible 
to the naked eye. 
In Flustra cribriformis * (Fig. 11), from Torres Straits, the 
fenestrated frond forms a beautiful spiral. Flustra fl or ea, from S. 
Australia, grows in the form of branching tufts of narrow spiral 
fronds. Electra pilosa [dry and spirit specimens exhibited] (Fig. 12) 
