A Revision of the Genus Aulacodiscus Ehrb. By J. Rattray. 341 



12 in O'Ol mm., 1/15 to 1/21 of radius broad, indistinct. Pro- 

 cesses 2 to 4, insertion 1/3 to 2/7 of radius from circumference, proximal 

 portion equal to distal, constriction median, wide, shallow, free ends 

 rounded, length about 5 times breadth, no space at their base. — Sch. 

 Atl., pi. civ. figs. 3, 4. 



The central space is larger as the number of processes is less. 

 Some valves from Simbirsk have the free ends of the processes more 

 knob-like than others. Transitional to the simpler species of the 

 section Eadiati. 



Habitat : Simbirsk Polirschiefer (Weissflog ! Eae !) ; Monterey- 

 stone (Cleve ! Weissflog !) ; Barbadoes (Firth !) ; Sysran deposit, 

 Siberia (Hardman !). 



A. parvulus sp. n. — Diam. 0"0675 mm. Surface flat to zone of 

 processes, slope to border gentle. Colour smoky grey, lighter 

 towards border. Central space rounded, about 1/27 of diam. broad, 

 hyaline. Markings polygonal, 6 in ■ 01 mm., decreasing but slightly 

 towards border, without interspaces. Primary rays inconspicuous, 

 rows in contact to their outer ends. Border hyaline, inner edge 

 distinct, about 1/18 of radius broad. Processes 5, symmetrical, 

 insertion about 1/4 of radius from circumference, large, constriction 

 median, shallow, free ends rounded. 



Habitat : Shell cleanings Nicobar Islands (Doeg !). 



A. Broivneii Norman, in Pritch. Inf., p. 844. — Diam. ' 06 to 

 • 0775 mm. Surface flat to zone of processes. Colour pale blue or 

 grey, light or dark grey at border. Central space irregular, 1/24 to 

 1/3(3 of diam. broad, hyaline, rarely reduced to an elongated clear line. 

 Markings rounded, towards centre more irregular, 5 in 0*01 mm., 

 rows sometimes slightly bent, at outer ends separated by narrow clear 

 spaces, secondary concentric bands obvious, sometimes confined to 

 elevated central portion or to periphery. Primary rays distinct, space 

 between rows narrow as on rest of surface. Border striae 12 to 14 

 in 0"01 mm., 1/30 to 1/36 of radius broad, sometimes a narrow clear 

 band at its inner edge. Processes 2 to 4, insertion 1/3 to 2/9 of 

 radius from circumference, proximal portion oval, with a rounded, faint, 

 obliquely placed mark on the corresponding side of all the processes 

 of same valve, distal larger spathulate, clear space at base small. 

 — Sch. Atl., pi. xxxvi. figs. 15-16 ; pi. cv. fig. 6. 



In specimens with 2 processes the concentric bands are most 

 obvious at periphery. In the presence of a faint oblique mark at 

 base of processes this species recalls A. barbadensis. It is allied to 

 the flatter forms of A. hiUcellyanus. 



Habitat: Monterey stone (Greville! Hardman! Stokes! Arnott!); 

 Santa Monica deposit (Kae !) ; marine algae, California (Kae !) ; shell 

 scrapings, California (Grove !) ; on Haliotis shell, South Sea Islands 

 (Hardman ! Weissflog !). 



A. Comber i Arnott, in Pritch. Inf., p. 844. — Diam. 0*11 to 

 • 265 mm. Surface flat to processes, rarely depressed at centre for 

 1/4 to 1/5 of radius. Colour lurid or pale to brownish grey araund 



