258 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 105 



the avicularium-bearing mucro which points away from the other 

 orifice corner. The suboral external avicularium is placed on the 

 median to oral side of this farthest mucro, so points at an angle of 

 approximately 30° downward and outward away from the orifice. 

 The inner avicularium is placed more or less transversely at the inner 

 side-front of the zoid, so it cannot be seen from the outside. External 

 avicularial mandible about as long as wide. Proximal border of 

 primary orifice divided and considerably distorted by a vertical, 

 diagonally directed frontal oral ledge. The most distinctive feature is 

 the presence of an extensive projecting peristomial cap. The second- 

 ary orifice is sometimes very asymmetrical. 



The species is named C. rossi because it was collected near Ross 

 Island, Antarctica. 



Zoarium: Only five sprigs, the longest of which is 28 mm. long, are 

 in the collection. The colony varies in color from a light dull tan to 

 ivory. The sprigs are narrow, tapelike, bilaminate, and one shows 

 the beginning of another branch. The colony surface is slightly 

 roughened, like a file, by the mucros. Orifices make tiny pits, just 

 visible to the naked eye. Colony width varies from 2 to 4 mm. and 

 its thickness is about 1 mm. at the tip of the sprig. The longest 

 sprig has about six nodes. The nodes (pi, 13, A) are not flexible but 

 are similar to those of the preceding species. The number of linear 

 rows of zooecia in an internode (area between nodes) ranges from 3 to 

 11, while the number of rows of zooecia across one face of the colony, 

 from edge to edge of an internode, varies from 6 to 13. 



Zooecia: Zooecial boundaries are externally unmarked. Ap- 

 proximate zooecial length, externally, from one orifice to the next was 

 1.08-2.160 mm. (average 1.606 mm.). Internally the zooecia are 

 shaped like inverted flasks (pi. 13, C). The channeled frontal wall is 

 0.202-0.374 mm. (average 0.274 mm.) thick at the upper center of the 

 zooecium. The deviating and variable channels terminate in external 

 frontal pores (pi. 13,B,D,H-J) of 0.022-0.122 mm. diameter at one 

 end and some of them in internal frontal and lateral pores at the other 

 end (pi. 13,C). Lateral and back walls are very thin, 0.014-0.022 

 mm. Lateral walls have a few large rosette plates near the mid- 

 region and numerous single pores along the edge bordering the frontal 

 wall. The back walls are flat, the lateral walls curve a bit, and the 

 frontal inner wall curves considerably. Zooecial dimensions, as 

 measured from the inner surface: width, from side wall to side wall, 

 0.187-0.389 mm. (average 0.299 mm.); thickness, from back wall to 

 outside of front wall, 0.518-0.720 mm. (average 0.619 mm). The two 

 calcareous processes over the end wall appear to be thinner than 

 those of the preceding species (see pis. 12,I,K; 13,C). 



