BRYOZOAN FAUNA OF VINCENTOWN LIMESAND 27 



Genus CRASSIMARGINATELLA Canu, 1900 



CRASSIMARGINATELLA INTERMEDIA, new species 



Plate 5, Figures 4r-7 



Description. — The zoarium encrusts fragments of shells and free 

 Bryozoa. The zooecia are distinct, separated by a deep furrow, 

 elliptical, elongated; the mural rim is thin distally and somewhat 

 enlarged at the base; it is salient, flat interiorly, and finely granu- 

 lated. The opesium is large, entire, of the same form as the zooe- 

 cium, finely crenulated. The ovicell is hyperstomial, not closed by 

 the operculum, globular, transverse, smooth, carinated, embedded 

 in the distal zooecium. The interzooecial avicularium is large, 

 sporadic, provided with a gymnocyst, primoserial, pyriform, ter- 

 minating in the form of the beak of a duck; its opesium is large 

 median, elliptical. The ancestrula is a small ordinary zooecium. 



Measurements. — 



[Ls = 0.54-0.66 mm. ~ . [7^ = 0.39-0.48 mm. 

 Zooecium {, _ __ n ... (Jpesium{ 7 „ no A 0>7 



[7.3 = 0.36-0.41 mm. L \lo = 0.23-0.37 mm. 



24-28 zooecia in 4 sq. mm. 



Variations. — The zooecia increase in size according to their dis- 

 tance from the ancestrula; our first measurements are those of the 

 average zooecia, the second of the marginal ones. 



The ovicells are quite typical ; their orifice placed above the mural 

 rim is easily visible on inclining the preparation slightly. When 

 the proximal border of the ovicell covers the distal border of the 

 mural rim, the observer may hesitate, but on dissection one can 

 note that the distal border is neither attenuated nor deformed and 

 that the opercular valve supported on it does not close the ovicell. 

 The presence of the longitudinal carina is not constant. 



Regenerated zooecia are abundant. Our figures present almost 

 all the possible cases of total regeneration, notably: (1) An ordi- 

 nary zooecium regenerated by an ordinary zooecium; (2) an ordi- 

 nary zooecium regenerated by an ovicelled zooecium; (3) an ovicelled 

 zooecium regenerated by an ordinary zooecium; and (4) an inter- 

 zooecial avicularium regenerated by an ordinary zooecium. We 

 have figured a case of cellular inversion appearing without any 

 apparent reason. 



The interzooecial avicularia are almost always primoserial, al- 

 though they rarely appear in a longitudinal series already formed. 

 They also serve as cells to fill in empty spaces in cases of irregu- 

 larity in the gemmation. Their number on a given surface is very 

 variable. They are indeed organs of adaptation whose presence is 

 regulated only by the necessity of the moment. Their dimensions are 

 variable and in harmony with those of adjacent zooecia. 



177635—33 3 



