PALMICELLARIA SKENEI. 381 



In its ordinary condition P. Skenei is distinguished by 

 broad, flat, somewhat palmate and rather short branches, 

 which expand slightly above, and seldom lie in the same 

 plane ; the surface is made rough and hispid by the nume- 

 rous tall mucronate processes which rise from the front 

 of the cells*. It is liable, however, to many changes of 

 habit ; and in the remarkable variety |3 (foliacea) it has 

 entirely lost its usual manner of growth. In this form it 

 appears as a continuous lamina, curved and twisted and 

 folded upon itself, with a deeply sinuated margin. So far 

 as external aspect goes, the contrast between this foliated 

 variety and the normal condition is complete and striking ; 

 but in the minute characters there is perfect agreement 

 between them. In the young zooecium there is no ele- 

 vation of the peristome, the orifice is on a level with the 

 general surface of the cell, and there is no trace of avicu- 

 laria; but with advancing growth the peristome rises, 

 and is carried outwards, projecting considerably, and at 

 its extremity in front the avicularium is developed, the 

 mucro ascending immediately below it. A secondary 

 orifice is thus formed, which incloses the primary, and 

 which differs from it widely in size and shape. 



The mucro is tall and acuminate, except on the cells 

 towards the base of the zoarium, where it is sometimes 

 blunt and rudimentary. Occasionally a mucro is deve- 

 loped on each side of the orifice, and bears an avicularium 

 on its inner surface at the base, or at times on its summit. 

 The latter variety is the Lepralia bicornis, Busk. Occa- 

 sionally the two processes are developed in a line with 

 the central mucro ; and we have then the variety tridens 

 of Busk. 



In some cases the zoarium glistens as if coated with 

 varninh. 



* "... densii ha.itilibus horrida." VIRGIL. 



