ANTARCTIC BRYOZOA — ROGICK 279 



The zooecial frontal wall is an olocyst overlaid by a pleurocyst. 

 The olocyst, seen in one zoid only (from "Rock 7") is a beautiful smooth 

 glistening white, with tiny bordering pores. The plem'ocyst is thick 

 •md patterned (pi. 20, A,G,H). It has one or two alternating rows of 

 iny slitlike peripheral pores which perforate the thick wall. The 

 )eristome, mucro, and ovicell are the most elevated parts of the frontal 

 .urface. 



Avicularia: Absent. 



Orifice: Both the primary and secondary orifices are very small, 

 learly cu"cular, and well raised above the rest of the frontal sm^face. 

 They are frontal in position, some distance from the distal end of the 

 jooecium. The thick but short peristome supports a mucro that is 

 I stout spike or flattened triangle (pi. 20,F,H). Delicate, hollow, 

 lyaline spines, usually 6 to 8 in number, arise from the thickened 

 3asal supports (pi. 20,C,H). When an ovicell is present the peristome 

 3ontinues at least partly across the ovicell rim and carries with it 

 ^hese spine bases (pi. 20,E,G). A small lyrula, occasionally simple but 

 lUsually with several peaks and points projectmg in various planes, is 

 in the primary orifice just back of the mucro (pi. 20,A,D,I,J). Figure 

 B is the most typical one. The lyrula of one young zoid (from Station 

 i4) was typically trifid when viewed from the front but when the 

 same zoid was tipped forward the lyrula looked flat as in Mucronella 

 ventricosa. 



OviCELLs: Nonporous, globose, comparatively small, thick-walled 

 and pushed back from the peristome. Their surface is roughened. 

 Peristomial spine bases may encroach upon their frontal rim. 



Distribution and ecology: A rock from Station 184, bryozoan 

 crusts of a reteporid and Smittina abditavicularis from Station 44, and 

 a rock arbitrarily labeled No. 7 (station unloiown) are substrates for 

 Mucronella crozetensis of the U. S. Navy collection. 



This species has been previously reported by Busk, Waters, and 

 Livingstone. Its longitudinal range so far extends from 89°15' W^. 

 (Waters) to 101°13' E. (Station 44), and its latitudinal range is from 

 46°47' S. (Busk) to 71°19' S. (Waters). It has been collected at 

 depths from 80 to 210 fathoms (Busk). 



Its substrates, in addition to gravel and rocks, include other 

 Bryozoa (reported by Rogick) and a valve of Terebratula (reported 

 by Busk). 



Affinities: This species is most closely related to if not an actual 

 variety of Mucronella ventricosa (Hassall) as pictured by Hincks 

 (1880, pi. 50, figs. 6-8) except for some differences in appearance and 

 number of oral spines; size, number of rows, and position of frontal 

 pores; and texture of pleurocyst and, especially, the lyrula. Osburn's 

 (1933, pi. 15, fig. 7) Mucronella ventricosa has the same textured 



