T!70 Transactions of the Society. 



on central area, but within this traceable to central space. Processes 

 4, insertion about 1/4 of radius from circumference, with slight 

 median constriction. 



Habitat : Sysran deposit (Grove !). 



A. Sturtii Kitton, Journ. Quek. Mic. CL, 1884, p. 17, pi. iv. fig. 1. 

 — "Valve sometimes elliptical, diam. 0*085 to 0*21 mm. Surface flat 

 to processes, sometimes slightly elevated around central space, a 

 distinct dark zone, bluntly angular at processes, 1/7 to 1/8 of radius 

 broad, with outer margin less sharply delined than inner, outside of 

 this slope to border gradual. Colour pale grey towards centre, pale 

 blue towards processes, elsewhere dark grey. Central space round 

 to bluntly quadrangular, 1/30 to 1/40 of diam. broad. Markings 

 round or bluntly angular, outlines indistinct, 4 to 5 in ■ 01 mm., rows 

 radial to subparallel, slight flexures towards periphery and processes. 

 Primary rays distinct, space between rows narrow. Border indistinct, 

 striae absent. Processes 3 to 5, insertion 1/5 to 1/7 of radius from 

 circumference, minute, simple, subcylindrical, constriction slight, 

 length about 4 times breadth. — Sch. Atl., pi. cvii. figs. 8, 9. 



The scar of the broken-off process is round or elliptical. 



Habitat : Japan oysters * (Kitton !) ; seaweed washings, Japan 

 (Grove !). 



A. racliatus\ Grev., Trans. Mic. Soc. Lond., 1864, p. 11, pi. i. fig. 4. 

 — Diam. O'll mm. Surface flat or rising gradually to about 2/3 of 

 radius, outer edge irregular, distinct ; highest zone about 1/7 of radius 

 broad, convex, well marked, round or faintly angular at processes, 

 outer edge abrupt irregular ; slope to border gentle. Colour trans- 

 parent, highest zone dark grey. Central space round to angular, 

 1/15 of diam. broad, hyaline, or with a few granules. Markings round 

 or compressed, 4 to 5 in • 01 mm., outlines faint, on highest zone 

 outlines almost inappreciable, but central dots prominent with long 

 axis oblique, and interspaces radially elongated conspicuous, hyaline, 

 with uneven edges. Primary rays inconspicuous, rows separated by a 

 narrow interspace. Border striae 12 in • 01 mm., inner edge distinct, 

 1/22 of diam. broad. Processes 5 or 6, insertion 2/11 of radius from 

 circumference, broken off; clear space at base well marked, with 

 edges uneven. 



The scar of the broken-off process is rounded. 



Habitat: Cambridge deposit, Barbadoes (Johnson !). 



A. pallidits Grev., Trans. Mic. Soc. Lond., 1863, p. 72, pi. v. 

 fig. 17. — Diam. 0*08 mm. Surface flat to about 3/4 of radius, 

 highest zone distinct, pentagonal, 1/8 of radius broad, inflations at 

 processes inappreciable ; slope to border gentle. Colour transparent, 

 highest zone pale grey. Central space round, about 1/16 of diam. 

 broad, indistinct, at its centre a small irregular more prominent mark 



* These oysters were exhibited at the Colonial Exhibition, and were purchased 

 by Mr. Sturt. 



t Not A. radiatus, as in Brightwell, Quart. Journ. Micr. Soc., 1860, p. 95, pi. v. 

 figs. 10a, 105. See p. 379. 



