62 



SHELL GALLERY. 



organ has arisen by a further modification of an avicularium, whereby 

 the horny lid of the latter has become a long bristle. The bristles 



Fig;. 10. 



Case 

 A 1,2. 



Case A 1. 



Case A 1. 



Scrupocellaria reptans. A. Creeping over seaweed, natural size ; B. Front 



surface, magnified. 



a, branched spine covering front of membranous area; b, 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 Caberea 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. 



Section B. Flustrina. — In this group the colonies form leafy 

 lamellse, crusts, etc., in which the individual cells are typically in 

 the form of oblong boxes with their front walls wholly or 

 partly membranous. ^z<!s^m/oZmcea has already been described. In 

 Mustra carlasea 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 noUlis 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 Jiorea, from S. 

 Australia, grows in the form of branching tufts of narrow spiral 

 fronds. Electra pilosa [dry and spirit specimens exhibited] (Fig. 12) 



