A Revision of the Genus Aidacodiscus Ehrb. By J. Rattray. 351 



evident. Central rosette inconspicuous, 1/10 to 1/19 of diam. broad. 

 Markings more irregular, more pearly, 3 in • 01 mm., decreasing 

 suddenly at 1/5 to 1/7 of radius from border, secondary subconcentric 

 rows towards centre indistinct. Primary rays with rows less divergent. 

 Border hyaline, 1/17 to 1/38 of radius broad, inner edge definite. 

 Processes 4, rarely 3, insertion 1/6 to 5/17 of radius from circum- 

 ference, larger, constriction median, wide, shallow, no clear space at 

 base.— PI. VI. fig. 8. 



The scar of broken-off process is narrow and elongate. 



Habitat : Oamaru deposit, New Zealand (Grove & Sturt ! Eae !). 



A. margaritaceus Ealfs, in Pritch. Inf., p. 814. — Diam. 0*1 to 

 0*415 mm. Surface flat to processes or to 1/2 of radius, sometimes 

 concave at centre, highest zone angular at processes, 1/8 to 1/3 of 

 radius broad. Colour pale grey, border darker. Central space 

 angular, elliptical, rarely sub-obsolete, 1/10 to 1/60 of diam. broad, 

 hyaline, rarely punctate. Markings rounded or polygonal, pearly, 

 3| in 01 mm., moniliform towards border, dot often unilateral, 

 interspaces hyaline. Primary rays with rows in contact or diverg- 

 ing from semiradius, sometimes interrupted. Border strife 8 in 

 • 01 mm., 1/30 to 1/40 of radius broad. Processes 3 to 12,* insertion 

 1/4 to 1/11 of radius from circumference, small, clavate, constriction 

 shallow, about 1/3 of length from base, clear space at base small, 

 length about 2J times breadth. — Sch. Atl., pi. xxxvii. figs. 4, 5 ; 

 pi. xcii. fig. 12 ; pi. civ. figs. 7, 8; pi. cv. figs. 1, 2, 4. A. crux 

 Ehrb. Mikrog., pi. xxxv. A. 16 fig. 2. A. samoensis Grun. 1883, 

 Moller, Preisverzeichniss Mikr. Prap. fide Cleve. A. crux var. 

 peruana Grun., Denk. Wien. At, 1884, p. 69 ; Sch. Atl., pi. xxxiii. 

 figs. 1-3. The scar of the broken-off process is oval. 



Habitat : Patos Island guano (Johnson ! Browne ! Weissflog !) ; 

 California guano (Greville ! Norman !) ; Mejillones, Peru (Kinker ! 

 Hardman !) ; Sta. Marta deposit (Hardman ! Weissflog !), Sta. Monica 

 deposit (Joshua !) ; Calvert Co., Maryland (Weissflog !) ; California 

 (Cleve ! Grundler !) ; New Caledonia (Kinker !) ; Sierra Leone (Hard- 

 man !) ; Eio Janeiro (Hardman ! Firth !) ; Java ex Holothurid edule 

 (Kinker ! Weissflog !) ; Samoa (Cleve !) ; Labuan (Weissflog ! Cleve !) ; 

 San Jose Pearl Islands (Cleve !). 



Var. Debyi, — A. Debyi Pant., Fossil. Bacil. Ung., p. 58, pi. xxv. 

 fig. 226. Diam. 0*205 to -6 mm. Surface flat for 3/8 of radius, 

 slope to border steep. Primary rays inconspicuous, the rows diverg- 

 ing for about outer 1/3 of length. Processes 4 to 11, insertion 1/5 

 to 1/9 of radius from circumference, much larger, free ends flattened, 

 proximal portion about 3/5 distal in breadth, clear space at base 

 small, length about 1£ times breadth. — Sch. Atl., pi. civ. fig. 9. 



Habitat : Mejillones, Peru (Kinker !) ; California Guano (Greville !) ; 

 Oamaru deposit (Grove & Sturt ! Eae !). 



Var. elongata. — Diam. • 375 mm. Surface rising gradually for 



* The number on valves of a single frustule is sometimes different, e. g. four on 

 the one, five on the other. 



