BRYOZOAN FAUNA OF VINCENTOWN LIMESAND 



63 



secondary aperture (peristomice) ; the distal shield appears to be 

 solid and formed by the upward prolongation of the apertural ring, 

 which ieplaces the distal pair of apertural spines. The avicularia, 

 a small apertural pair, are carried upon the secondary apertural 

 ring and replacing the proximal pair of apertural spines, directed 

 toward the center of 

 the aperture of the 

 zooecium it accom- 

 panies somewhat 

 elongate with rather 

 blunt apertures. 



Remarks. — Were 

 it not for the pres- 

 ence of avicularia 

 and the somewhat 

 smaller size, Sticho- 

 cados compositus 

 might have been de- 

 rived from S. verru- 

 culosus (Maastrich- 

 tian). On the as- 

 sumption, however, 

 that S. verruculosus 

 was derived from 

 Carydiopora by the 

 loss of avicularia as 

 well as by the acqui- 

 sition of a secondary 

 aperture, S. compos- 

 itus, which has not 

 yet lost its avicularia, 

 is more primitive in 

 this respect. 



Measurements. — 



~ . \Lz = 0.5 mm. . f/m=0.11-0.13 mm. 



Zooeciaj /3 = (U ^ Apertura | /a = (U _ ail mm . 



24 zooecia in 4 sq. mm. 

 Variations and structure. — Lang, 1922, has given a masterly inter- 

 pretation of the structure of the curious genus Stichocados Marsson, 

 1887, and it required all his experience in the study of the Cribri- 

 morphs to understand its complexities. He had for this study only 

 the four figured cells (pi. 4, fig. 3), which were sufficient for his 

 schematic figure 57. So it is not surprising that he omitted the for- 



D 



Figure 1. — A, Stichocad-os compofitus Lang, 191G, diagram 

 of a zooecium (X 75) showing the frontal structure ; 

 B, C, Hesperopora occidental^ Lang, 1916, diagram of 

 an ancestrular and a normal zooecium ( X 75) ; D, Tri- 

 cephalopora prolifera Gabb and Horn, 1S62, zooecium 

 ( X 75) showing general structure ; E, Diacanthopora 

 abbottii Gabb and Horn, 1862, zooecium (X75) — the 

 talon of the avicularium should be placed on the mural 

 rim of the adjacent zooecium. (After Lang, 1922.) 



