ART. 14 FOSSIL AND RECENT BRYOZOA CANU AND BASSLER 81 



cium a large orbicular cribriform area closed by the ectocyst. It is a 



radicular septule. 



,, ^ A X J^a = 0.22-0.25 mm. 



Measurements. — Aperturei , ^ _ ^ 



^ lZa = 0.25 mm. 



„ . fZ2=1.00 mm. 

 Zooeciai, ^ ^_ » _- 



Us = 0.65-0.70 mm. 



Structure. — The operculum is light colored and bell-shaped. The 

 marginal band is very narrow; the proximal border is indecisive, for 

 it is attached to the compensatrix. We are obliged, in order to fig- 

 ure it, to indicate only the line of rotation. Like the aperture, the 

 operculum is elongated or transverse. 



In the interior the two cardelles are quite visible ; they correspond 

 exactly to the axis of rotation of the operculum, which also repre- 

 sents only the portion covering the anter. The tremopores are quite 

 visible and numerous. 



The dorsal admirably shows by transparency the structure of the 

 cribriform area. The latter appears as a large multiporous septule. 

 The pores are unequal in size and variable in number (10 to 20). 

 Exteriorily there is a concavity closed by the ectocyst and from 

 which large radicells sometime spring. 



The ovicell is not of the same nature as the frontal. This feature 

 is, moreover, one of the family characters. In the Escharellidae, 

 for example, the ovicell is developed between the olocyst and the 

 pleurocyst or tremocyst of the distal zooecium. Here, on the con- 

 trary, the ovicell has special walls; the distal zooecium is completely 

 calcified when it is formed. The operculum does not close the ovi- 

 cell throughout its life, but in opening it permits the passage of the 

 eggs in closing exactly the orifice of the ovicell. However, on our 

 dissected specimens we are not positively certain of the exactness of 

 this observation. 



Variations. — The small apertural avicularia are very constant. 

 They are elliptical, but their orientation is quite variable. They 

 must exercise the function of the oral glands which do not exist in 

 this family. The large avicularium is zooecial; its presence is incon- 

 stant and its dimensions are variable. When one of the small aper- 

 tural avicularia becomes very large, the large avicularium does not 

 develop. 



The zoarium often has the form of a hollow horn. The radicells 

 are rarely present on the interior face. The latter is almost always 

 incrusted by small species of bryozoa and notably by Gemellipora 

 ehurnea Smitt, 1872, which thus finds safe shelter to protect its 

 especially fragile zoarium. 



The separating thread of the cells is constant but it is very salient 

 and quite visible on the old, strongly calcified zooecia. 

 58513—28 6 



