A Revision of the Genus Aulacodiscus Ehrb. By J. Rattray. 379 



The scar of broken-off process is large and irregularly oval. 



Habitat : Cambridge deposit, Barbadoes (Johnson ! Norman !). 



Yar. clirupta Grove & Sturt M.S. — Diam. 0*035 mm. Surface 

 flat from centre to border, primary rays not elevated. Colour smoky 

 grey, darker at border. Central space about 1/14 of diam. broad. 

 Markings quadrate, 3^ to 4 in 0*01 mm., rows sometimes subradial, 

 moniliform at border. Primary rays distinct, rows diverging widely 

 almost from central space. Border with inner edge indistinct. Pro- 

 cesses 6, insertion about 1/7 of radius from circumference. — PI. VI. 



The scar of broken-off process is mmute, oval. 



Habitat : Oamaru deposit (Grove !). 



A. lucidus sp. n. — Diam. 0*1135 to 0*175 mm. Surface flat for 

 2/7 to 1/2 of radius, primary rays slightly elevated, compartments 

 with a wide flat portion at border. Colour light grey. Central space 

 minute, about 1/65 of diam. broad. Markings polygonal, 4 in 0-01 

 mm., rows radial, in wide curves towards and around processes. 

 Primary rays distinct, rows with markings larger in outer than in 

 inner half, diverging but slightly at outer ends. Border striae irregu- 

 lar, 5 to 8 in -01 mm., inner edge irregular. Processes 8, insertion 

 about 1/4 to 1/5 of radius from circumference, proximal portion 

 smaller than round knob-like distal; clear space at base absent. — 

 PL V. fig. 3. 



Habitat : Barbadoes deposit (Han well ! Grove !). 



A. coronatus Grove' MS. — Diam. 0' 0925 mm. Surface flat for 

 about 1/4 of radius, thence sloping slightly to zone of processes, 

 almost flat around border. Primary rays on a level with adjacent 

 areas. Colour subhyaline, darker at centre and processes. Central 

 space indistinct. Markings polygonal, 5 in 0'01 mm. on central 

 portion, 8 to 10 in "01 mm. from zone of processes to border, without 

 interspaces ; rows straight, radial. Primary rays inconspicuous, the 

 rows in contact. Border indistinct, about 1/19 of radius broad. 

 Processes 9, 11/19 of radius from circumference, proximal portion 

 small, distal knob-like ; clear space at their base large. 



Habitat : Jackson's Paddock, Oamaru (W. J. Gray !). 



I am unacquainted with " Aulacodiscus californicus Bail. Coll." 

 recorded by Habirshaw in the second edition of his Catalogue. The 

 name is only recorded here, and remains a nomen nudum. 



Auliscus sculptus Ealfs and Eupodiscus radiatus Bail, were in 

 error printed in Brightwell's paper (Quart. Journ. Mic. Soc, 1860, 

 p. 94) as species of Aulacodiscus, but the errors were corrected in the 

 errata on p. 139 of the same volume. 



The valve from the Barbadoes deposit, placed doubtfully by 

 Greville in Aulacodiscus as A (?) paradoxus (Trans. Mic. Soc. Lond. 

 1863, p. 72, pi. v. fig. 18), was subsequently referred by him to 

 Omplialopelta, and recorded as such in the copy of his memoir in the 

 possession of Mr. Kitton. It is really a species of the genus 

 Actinoptychus. 



