A REVISION OF THE GRNQS STEGANOPORELLA. 279 



I have found very little variation in this species, my 

 specimens of which have, however, come from practically 

 one locality. The characters of the opercula are remarkably 

 constant. It need hardly be pointed out that where a zooecium 

 is restricted in its growth by want of room its operculum 

 may be abnormally small. Leaving these cases out of accouiit, 

 the diameter of a opercula varies between 490 and 640 fx, with 

 an average of about 525 /ll ; that of b opercula between 500 

 and 620 fx, with an average of about 550 fx. 



11. S. magnilabris, Busk. Figs. 10, 31, 44—46. 



Membranipora grandis. Busk, ' Cat. Mar. Polyzoa 

 Brit. Mus.,' i, 1852, p. vi (explanation of pi. Ixv), 

 pi. Ixv, fig. 4. 



Membranipora magnilabris, Busk, ibid., ii, 1854, 

 p. 62 (part), 113, ? Haswell, ' Proc. Linn. Soc. 

 N.S. Wales,^ v, 1881, p. 38. 



Steginoporella elegans, Smitt, ' Svenska Ak. 

 Handl.,' xi. No. 4, 1873, p. 15, pi. iv, figs. 96—101. 



Steganoporella magnilabris, Hincks, * Ann. Nat. 

 Hist.' (5), ix, 1882, p. 123 [Abrolhos I., Singa- 

 pore], ? pi. V, figs. 8, 8a; Busk, 'Challenger 

 Rep.,' pt. XXX, 1884, pp. 75, 76 (woodcuts, fig. 4), 

 pi. xxiii, figs. 2, 2a; ? Ortmann, 'Arch. f. 

 Naturg.,' Ivi, 1, 1890, p. 30, pi. ii, fig. 7. 



B zooecia considerably larger than the a zooecia. Crypto- 

 cyst descending at right angles, without or with thickened 

 angulation, to join the basal wall. Median process usually 

 with high walls, and often with a somewhat thickened distal 

 edge supporting the basal sclerite of the operculum ; its 

 cavity moderately deep (exceptionally shallow or absent), its 

 floor wide, formed by the convex roof of the tube. Opening 

 of tube vertical, not or hardly visible from above, complete 

 basally, or completed by the basal wall of the zooecium, oral 

 shelf distinct in both a and b, larger in b, where the cavity 

 between the shelf and the oral arch is specially large, b 



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