278 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 105 



This genus is represented by one species in the present Antarctic 

 collection. 



Diagnosis: Zoarium encrusting; frontal areolate; avicularia absent; 

 primary orifice smittinoid, with lyrula; secondary orifice with peri- 

 stome; umbo som.etimes present; ovicell hyperstomial and imperforate. 



Genotype: Lepralia peachii Johnston, 1847 (p. 315). 



Mucronella crozetensis (Waters) 



Plate 20 



Mucronella ventricosa var. midtispinata Busk, 1884, pp. 160-161, pi. 22, fig. 11. 

 Smittia crozetensis (new name) Waters, 1904, p. 64, pi. 8, fig. 15a,b. 

 Mucronetla crozetensis, Canu and Bassler, 1920, p. 475. — Livingstone, 1928, p. 66. 



Diagnosis: Zoarium encrusting. Zooecia ovate or hexagonal, 

 narrowing suddenly upward to the narrow elevated peristome. Stout 

 pointed mucro in front of small lyrula. Lyrula bifid, trifid, or with I 

 more points projecting in various planes. No cardelles. Primary and 

 secondary orifices otherwise nearly circular and small. Pleurocyst 

 frontal with one or two rows of tiny slitlike peripheral pores. Basei 

 partly membranous, partly calcareous. Ovicell small, globose, non- 

 porous, slanting back from peristome. Peristomial spines usually 6( 

 to 8, the bases of some encroaching on the ovicell front. 



Measurements: Minimum to maximum and average measure-: 

 ments, in millimeters, are given below (for explanation see p. 271). 1 



Z-L, 0.432-1.11 mm. (0.802) Se-Or-W, 0.115-0.144 (0.135, inside) 



Z-W, 0.346-0.740 mm. (0.579) Ov-L, 0.230-0.274 (0.258) -' 



Pr-Or-L, 0.115-0.130 (0.117) Ov-W, 0.252-0.389 (0.318) ' 



Pr-Or-W, 0.122-0.158 (0.139) Ly-L, 0.022-0.043 (0.038) 



Se-Or-L, 0.202-0.252 (0.224, outside) Ly-W, 0.040-0.069 (0.047, at base) : 



Se-Or-W, 0.209-0.259 (0.233, outside) Ly-W, 0.058-0.086 (0.069, at top) 

 Se-Or-L, 0.101-0.130 (0.114, inside) ' 'f 



Ml 



Zoarium: Dull, white to ivory, encrusting, attached to a rocky 

 substratum by calcareous zooecial rims and membranous bases. 



Zooecia: Distinct, ovate to hexagonal, highly convex, mound- 

 shaped, porcellanous. Mural rims depressed. Each zooecium arises 

 from a base that is centrally membranous and peripherally calcareous 

 (pi. 20, H). The membranous bases of neighboring zoids are con- 

 nected by numerous, slender, yellow to brown canals (pi. 20, D,K)., 

 Waters did not report them for M. crozetensis but in Lepralia jrigida 

 did find only one tube to each neighbormg zoid (1904, p. 47, pi. 8, fig.; 

 9). Mucronella crozetensis has 5 to 10 tubules connecting with eachl 

 neighboring zoid. In Mucronella, canals leaving the distal half of ai 

 zoid have constrictions within the confines of that zoid, but those 

 leaving the proximal half of the same zoid do not have them (pi. 20,K). 

 Several small fiber bundles (parietal muscles?) attach to the basal 

 membrane at the more distal sides. 



M 



