A REVISION OF THK GENUS STKGANOPORl'lLLA. 259 



dark, indicating- the base of the tooth-bearing or main 

 sclerite. Both these dark lines are in the plane of the outer 

 surface of the operculum, and g is accordingly the origin of 

 the sub-basal sclerite (seen from the inside in fig. 24). The 

 real form of the sclerites can be well made out in these large 

 and thick opercula in dry specimens seen from the inner side. 

 The edge h of the sub-basal sclerite stands up above the 

 surface in this view, the sclerite sloping from its origin g 

 obliquely to its most prominent part h. This is continued 

 into the projecting proximal spout i, in which each of the 

 halves of the main sclerite ends. The proximal tooth of 

 each side is connected by a buttress with the distal end of 

 the sub-basal sclerite. The main sclerite is very convex on 

 the proximal side of the proximal tooth, sloping from here to 

 the base of the operculum, where the main sclerite runs into 

 the general level of the operculum. In optical sections of 

 Canada balsam preparations the proximal part of the main 

 sclerite appears as two parallel bars, the most prominent 

 part being thinner than its sides. 



The edge h of the operculum rests on the distal border of 

 the calcareous median pi'ocess, the projecting points of the 

 condyles fitting into the angles where h turns proximally. 



The opercula do not vary much. Their average diameter 

 is about 550 ju, the size of the specimen figured. 



7. S. neozelanica. Busk. 



Synonyms of Typical or Vincularian Form. Figs. 4, 25, 30. 

 Vincularia neozelanica. Busk, 'Quart. Journ.Micr. 

 Sci.' (N. S.), i, 18G1, p. 155, pi. xxxiv, figs. 5, 5 a; 

 and 'Chall. Rep.,' pt. xxx, 1884, p. 76; Hutton, 

 'Man. New Zealand Mollusca,' 1880, p. 189. 

 Steganoporella neozelanica, Hincks, ' Ann. Nat. 

 Hist.' (5), ix, 1882, p. 119, and (6), xi, 1893, p. 

 175 j Waters, "^ Quart. Journ. Geol. Soc.,' xli, 

 1885, p. 292, and xliii, 1887, p. 50; 'Chall. Rep.,' 

 pt. Ixxix, 1888, p. 14, pi. ii, fig. 32 (or ? var. 



