A Revision of the Genus Aulacodiscus Ehrb. By J. Rattray. 353 



The scar of the broken-off process is elliptical. 



Habitat: Calvert Co., Maryland (Kinker ! Cleve !) ; Nottingham 

 deposit, Maryland (Greville ! Norman ! Johnson ! Cleve ! Weissflog !) ; 

 Bermuda tripoli (Greville ! Weissflog !). 



Var. distincta. — A. Molten war. Sch. Atl., pi. xcii. fig. 13. — Surface 

 showing an elevated polygonal central area with distinct outwardly con- 

 cave edges. Central space sharply defined, about 1 /35 of diam. broad. 

 Markings somewhat smaller than in var. Molleri (fid. Sch.). Primary 

 rays conspicuous, the markings in the rows with longer axis at right 

 angles to length of ray. Border with inner edge indistinct, more 

 opaque. Processes 5, insertion about 1/4 of radius from circum- 

 ference, clear space at base well marked. 



Habitat : Nottingham deposit (Janisch). 



Var. inconsjncua. — Diam. ■ 1125 to • 2 mm. Central space 3-4- 

 angled, finely punctate. Markings 2 ^ to 4 in " 01 mm., increasing for 

 about 7/8 of radius, then decreasing suddenly to border. Primary 

 rays indistinct. Processes 7, insertion 1/10 of radius from circum- 

 ference, as small conical protuberances with rounded ends. — PI. VI. 

 %. 3. 



Habitat : New South Wales (R. Rattray !) ; Sydney (Cleve !). 



Var. tenera. — A. crux var. tenera Witt, Simb. Polirsch., p. 19, 

 pi. vi. fig. 10. Diam. ' 095 to • 1125 mm. Surface flat to processes. 

 Central space round, 1/38 of diam. broad. Markings 8 in • 01 mm., 

 rows deflected at processes. Primary rays distinct. Processes 3 or 

 4, minute, insertion about 1/3 of radius from circumference. — Sch. 

 Atl., pi. cii. fig. 4. 



Habitat : Chincha Island guano (Arnott !) ; Haliotis shell 

 scrapings, California (Weissflog !) ; Simbirsk Polirschiefer (Witt !). 



A. scaler Ralfs, in Pritch. Inf., p. 844.— Diam. • 08 to • 27 mm. 

 Surface flat from centre to processes, sides convex on compartments. 

 Colour light, lurid. Central space angular, 1/34 to 1/84 of diam. 

 broad, hyaline. Markings polygonal, 4 in " 01 mm. decreasing sud- 

 denly towards border. Apiculi numerous, short, irregularly placed, 

 sometimes chiefly between processes, rare outside of latter. Primary 

 rays distinct, rows in contact or diverging but little at outer ends. 

 Border striae 6 to 8 in 0*01 mm., 1/14 to 1/42 of radius broad. 

 Processes 3 to 5, insertion 1/4 to 1/5 of radius from circumference, 

 hourglass-shaped, constriction well marked, length 2 to 2^ times 

 breadth. — Sch. Atl., pi. xxxiii. figs. 4-8. A. crux Ehrb. var., 

 Habirshaw Cat. Diat., § Aulacodiscus ; A. ternatus Janisch, Abh. 

 Sch. Ges. vater. Cult., 1861, p. 161, pi. ii. fig. 4; A. crux Janisch 

 (not Ehrb.), ibid. 1861, p. 161, pi. ii. figs. 1-3; 1862, pi. ia. fig. 12 ; 

 A. quinarius Janisch, ibid., 1861, p. 162. The scar of the broken-off 

 process is elliptical. 



Habitat : Peruvian guano (Ralfs ! Macrae ! Greville ! Johnson ! 

 Weissflog ! Schmidt, Janisch, Browne) ; North Celebes, Ichaboe, and 

 Chincha guanos (O'Meara !). 



1888. 2 c 



