I 



ANTARCTIC BRYOZOA — ROGICK 245 



,rhe mural rims (external wall boundaries) of young zooecia (pi. 9,B). 

 ire thin and salient but become depressed in older ones as calcification 

 oecomes heavier. As calcification progresses, raised cryptocyst ridges 

 ivhich form a horseshoe-shaped arch (pi. 9,B) above and around the 

 orifice change to two winglike projections or alae, one on each side of 

 the orifice, like the blinders on a harness (pi. 8,E). They jut out so 

 prominently that they are the most conspicuous characters of the 

 colony, being recognizable even to the unaided eye. Their height is 

 from 0.158 to 0.230 mm. (average 0.199 mm.), their thickness at the 

 tip is from 0.043 to 0.058 mm. (average 0.053 mm.) and their length is 

 'from 0.259 to 0.331 mm. (average 0.305 mm.). Their edges are 

 beaded. They are transversely striated, almost fluted at the edge. 

 The parallel striations are due to the alignment of small tubercles into 

 iclose rows along these alae (pi. 8,E). Parenthesis-like chitinous lines 

 were not seen about the orifice. The rest of the frontal is depressed 

 but closely tuberculate. The mural rim in older zooecia is depressed. 

 The cryptocyst slopes up from it a bit and then slopes gently down to 

 the depressed central region in which is located the orifice. The 

 orifice is a slight distance from the distal mural arch or cornice and 

 occupies a considerable amount of the frontal area (pi. 9,B). The 

 orifice length is about one-third to two-fifths that of the visible zooecial 

 length. 



Zooecial orifice. The orifice is longer than wide, curved distally, 

 the lateral sides about parallel, the proximal edge slightly concave. 

 Deep within it and arising from a calcareous ledge that originates 

 inside the proximal orifice border are two prominent conical condyles 

 (pi. 9,B). These fit into oval depressions of the operculum (pi. 

 9,D,E). The operculum is from 0.216 to 0.259 mm. (average 0.238 

 mm.) long and from 0.130 to 0.173 mm. (average 0.156 mm.) wide. 

 The chitinous operculum completely fits the orifice. Its inner border 

 has a partial flange extending into a heavier flange for muscle attach- 

 ment at the two nearly parallel sides (pi. 9,E). At the two proximal 

 corners are the oval transparent areas or depressions for the condjdes. 

 The heavy chitinous flange thins out at the distal and proximal 

 borders of the operculum. 



OvicELLs: The ovicell is salient, endotoichal, shallow, tipped back 

 a bit, shaped externally like an acorn cup or Viking helmet and covered 

 with small, closely set tubercles (pi. 8,E). It nestles partly between 

 and beneath the side walls of the neighboring zoids in such a way that 

 the cryptocyst ridges, or alae, of the neighboring zoids form a pair of 

 wings on the ovicell. The opening into the ovicell is broadly ellip- 

 soidal and some distance above the orifice of the zooecium. The 

 ovicell length is difficult to estimate because of the overgrowth of 

 neighboring zooecia but it seems to be from 0.216 to 0.331 mm. 



