A Revision of the Genus Aulacodiscus Ehrb. By J. Rattray. 343 



The scar of the broken process is irregularly obovate. Allied to 

 A. Comberi. 



Habitat : Szent Peter deposit (Pantocsek !) 



A. minutus sp. n. Cestodiscus or Aulacodiscus ? Sch. Atl., pi. 

 lviii. fig. 34. — Diam. about 0*025 mm. Surface flat to zone of 

 processes, slope to border gentle. Colour pale grey (?) Central space 

 absent. Markings rounded granular, irregular at centre, in subradial 

 rows to processes. Interspaces hyaline. Primary rays distinct, rows 

 separated by a wide interspace of uniform breadth. Border striae 

 distinct, 8 in 0*01 mm., about 1/9 of radius broad. Processes 14, 

 insertion about 1/9 of radius from circumference, consisting of a 

 single portion with rounded ends. 



Habitat : Monterey (Weissflog). 



§ 2. Tenerrimi. 



Surface flat. Central space hyaline or with faint grey tinge. 

 Primary rays distinct. Border hyaline. Processes minute. 



A. exiguus Witt., Simb. Polirsch., p. 19, pi. viii. fig. 6. — Diam. 

 0*03 mm. Colour almost hyaline, the areas about primary rays a 

 little darker. Central space round, about 1/6 of diam. broad, tinged 

 light grey, outside of this a clear narrow band with a short conical 

 clear space extending into middle of apex of each compartment for 

 about 1/6 of radius, and forming a distinct stellate figure. Markings 

 unresolved. Primary rays with the rows undifferentiated, the inter- 

 spaces surrounding at peripheral ends the bases of processes. Processes 

 5, subsymmetrical, insertion about 1/4 of radius from circumference 

 as minute radially elongate narrow marks. — Sch. Atl., pi. ci. fig. 12. 



Habitat : Simbirsk Polirschiefer (Weissflog !). 



Var. undulata. — Diam. 0'06 mm. Central area about 1/5 of 

 diam. broad, a broader clear line passing from it into apex of each 

 compartment, with edges more irregular. Markings larger, as close 

 minute puncta, most evident at edge of primary rays, outer edge of 

 sculptured area undulate, with sides convex at processes and concave 

 on compartments. Primary rays 9, symmetrical, insertion about 1/12 

 of radius from circumference. Border with a single band of minute 

 puncta, within it a clear area, widest at middle of compartments. — 

 PI. VI. fig. 7. 



Habitat : Oamaru deposit (Hanwell !). 



A. barbadensis Pialfs, in Pritch. Inf., p. 939. — Diam. ■ 045 to 

 • 0825 mm. Colour pale smoky grey. Central space round to 

 4-angled, 1/12 to 1/17 of diam. broad, edges uneven, with sides at 

 right angles to directions of primary rays. Markings polygonal, 

 12 in 0'01 mm., without interspaces, less regular near central space, 

 rows radial, secondary rows irregularly concentric towards centre, 

 minute apiculi sometimes present, except on an area at middle of each 

 compartment in zone of processes similar to the clear area at base of 

 processes on same valve. Primary rays with indistinct rows. Border 



