296 SIDNEY y. IfAiJMHR. 



U 111 b nail la pavonolla, Alder ( = Mu c roiiulla 

 pa voiiella^ aiictt.^). 



The structure of tlie adult zooecium (fig. 10) c1osl% rc- 

 seniblcs that of U. verrucosa, and I venture to place the 

 two species iu the same genus. There is no umbo nor median 

 avicularium, but the frontal shi(^ld ends in a rounded median 

 lobe which is not raised above the level of the rest of the 

 shield. Each of its latei-al shoulders (/. 67i. (?.) bears a con- 

 spicuous avicularium {avic). Its free surface rises into a 

 series of radial buttresses, and the areolas {ar.) between these 

 communicate with the general body-cavity by pores arranged 

 as in U. verrucosa. My preparations show with great 

 distinctness that cords of living tissue {,r) traverse these 

 pores, and unite to form a continuous sheet of living substance 

 (indicated by the brilliantly staiiied nuclei) which overspreads 

 the entire frontal shield even in old zooocia. The basal wall 

 is not provided e;cternally with a living membrane. 



It is well known that the front surface of Cheilostome 

 zooccia may alter greatly with age. The original pattern 

 may become lost, the thickness of the wall may increase very 

 greatly, and the orifices of the zooccia may finally be 

 completely covei-ed by secondary calcification. All these 

 changes can be understood when it is realised that the frontal 

 shield of an Escharine Cheilostome is covered by living 

 tissue. Milne-Edwards (1830, p. 27), in discussing the 

 alterations which take place with ago in l^^scharine forms, 

 came to the conclusion that the calcareous matter Avas a 

 living tissue which grows like a bone. (Joldstein (1880, 

 p. 48) has stated that in Mucronella ellerii the brilliant 

 scarlet colour " seems to bo located in a fleshy ej)idermis, 

 with which the stony polyzoary is coated." This is the 

 "epitheca" of many authors, commonly seen in dry prepara- 

 tions as a membiane overspreading the calcareous frontal 

 shield, and consisting, iu reality, of an external cuticle and 

 subjacent living tissue. 



' Uincks (ISSO^ |> o7C.. 



