A Revision of the Genus Aulacodiscus Ehrb. By J. Rattray. 377 



A. Beeverise Johnson, Grove & Start, ibid., p. 9. A. Comheri var. 

 oamaruensis Grove & Stout, ibid., p. 140. 



Habitat: Oamaru deposit (Grove & Start ! Bucknal!). 



Var. convexa. A. convexus Grove & Shirt, ibid., p. 140, pi. xii. 

 fig. 32. — Valve elliptical. Diam. ■ 0875 to • 09 mm. Surface flat 

 to about 1/4 to 2/3 of radius. Colour pale bluish at centre. Central 

 space 1/36 to 1/40 of diam. broad, sometimes replaced by a faint rosette. 

 Processes 3, insertion about 1/3 to 1/5 of radius from circumference, 

 length about 1| breadth, clear space at base minute. 



Habitat : Oamaru deposit (Grove & Sturt !). 



A. sollittianus Norman, Trans. Mic. Soc. Lond., 1861, p. 7, pi. ii. 

 fig. 5. — Diam. 0'0825 to 0'22 mm. Surface depressed at centre, 

 rising to highest zone just within processes, this zone angular at pro- 

 cesses, sides concave, slope to border gentle, rarely showing several (5) 

 angular zones. Colour pale grey, darker at middle of compartments 

 and at outer edge of highest zone. Central space round, 1/90 of diam. 

 broad, hyaline, with rosette round or angular, 1/18 to 1/20 of diam. 

 broad. Markings 4 in • 01 mm., central dot faint, interspaces absent, 

 rows curved around processes, hence at centre of periphery of com- 

 partments a V-shaped area frequent, secondary oblique rows distinct. 

 Primary rays with markings increasing in outer half. Border striae 

 4 to 6 in 01 mm., about 1/30 of radius broad. Processes 4 to 6, 

 insertion 1/3 to 1/4 of radius from circumference, large, irregularly 

 hourglass-shaped, proximal portion smaller than distal, constriction 

 towards base, free ends rounded, length about twice greatest breadth, 

 clear space at base large. — Sch. Atl., pi. xxxiii. figs. 11, 13; pi. cii. 

 fig. 5 ; pi. ciii. fig. 3. 



Habitat : Nottingham deposit (Norman, Hardman ! O'Meara ! 

 Cleve). 



Var. nova-zealandica Grove & Sturt, Journ. Quek. Mic. CI., 

 1887, p. 9, pi. iii. fig. 10.— I)iam. 0'125 to 0-225 mm. Surface 

 highest and slightly convex at centre, median area uniformly depressed, 

 its angles rounded close to border, periphery flat. Central space 

 minute, no rosette. Markings 4^ to 5 in • 01 mm., on inner portion 

 small apiculi sometimes present. Primary rays with markings equal 

 or decreasing on outer half to processes. Border striae. 10 to 12 

 in 0'01 mm., 1/12 to 1/21 of radius broad, secondary oblique lines 

 distinct. Processes 3, insertion 2/5 to 3/8 of radius from circum- 

 ference, larger distal portion rounded, 2 to 1\ times as broad as 

 proximal, constriction deep. 



Habitat : Oamaru deposit (Grove & Sturt !). 



Var. protuberans. — Diam. • 2 mm. Surface with low inflations 

 about outer ends of primary rays, outer edge of highest zone concave 

 between processes, abrupt, a fiat level elliptical area at outer end of 

 each compartment. Central rosette 1/20 of diam. broad. Markings, 

 apiculi numerous. Primary rays with markings increasing still more 

 towards processes. Processes 6, insertion 1/4 of radius from circum- 

 ference, smaller, constriction submedian, length about twice breadth. 



