A Revision of the Genus Aulacodiscus Ehrb. By J. Rattray. 339 



and O'Meara, Hauck and Bichter's ' Phykotkeka Universalis,' and 

 H. L. Smith's ' Diatomacearum Species Typicae,' and have through 

 the great kindness of Mr. E. Grove, Dr. James Eae, Dr. John Murray, 

 Mr. Julien Deby, Mr. Laurence Hardman, Mr. Kitton, Mr. William 

 A. Firth, Mr. Doeg, Dr. Griffin, Dr. Gray, Herr E. Weissflog, 

 Dr. Otto N. Witt, Dr. Pantocsek, and Herr Kinker, been able to ex- 

 amine the specimens from their private collections. Prof. Wittrock 

 has also kindly forwarded to me the preparations belonging to 

 Prof. P. T. Cleve, preserved in the Eoyal Botanical Museum, Stock- 

 holm. 



Aulacodiscus Ehrb. emend., Ehrb. Mon. Ber. Ak., 1844, p. 73. — 

 Valve circular, rarely polygonal. Surface flat, crateriform, or with a 

 raised zone: inflations small and mammillate beneath processes, or 

 large and cuneate along primary rays, sometimes absent. Colour trans- 

 parent, grey or lurid. Central space irregular or round, hyaline or 

 punctate, filled in by a rosette, or absent. Markings round, oval, or 

 angular, sometimes pearly, in rows straight or slightly curved, radial 

 or parallel within the compartments, and forming secondary oblique 

 or concentric lines; interspaces hyaline or punctate. Primary rays 

 distinct, rarely inconspicuous, on a level with or raised above adjoining 

 area, the rows diverging, rarely in contact. Border with radial or 

 oblique, rarely moniliform striae, sometimes hyaline, usually distinct. 

 Processes 1 to 45, inserted near border, conspicuous or small, some- 

 times absent. — Tripodiscus Ehrb. Abh. Ber. Ak., 1839, p. 159; 

 Tetrapodiscus Ehrb. Mon. Ber. Ak., 1843, p. 166 ; Pentapodiscus 

 Ehrb., ibid. ; Podiscus Bail. Amer. Journ. ScL, 1844, vol. xlvi. p. 137 ; 

 Eupodiseus Ehrb. pro parte, Mon. Ber. Ak., 1844, p. 73. 



§ 1. COMPLANATI. 



Surface flat to 1/3 of radius or onwards to processes. Markings in 

 radial straight rows. Primary rays not elevated. 



A. suspectus Sch., Atl., pi. xxxvi. figs. 17, 18. — Diam. 0*05 to 

 0*075 mm. Surface flat almost to border. Colour dark brown on 

 median zone, and light brownish-grey near border. Central space 

 irregularly angular, 1/12 to 1/15 of diam. broad, hyaline. Markings 

 rounded, granular, 6 in 0-01 mm., decreasing regularly outwards, 

 towards central space their faint outlines visible. Primary rays 

 3 or 4, indistinct, straight, extending for 1/7 to 1/10 of radius from 

 circumference, the rows closely apposed. Border indistinct, non- 

 striated. Processes absent, no clear area at outer ends of primary rays. 



Allied to Coscinodiscus. Moller, according to Schmidt, makes this 

 a var. of Coscinodiscus punctulatus Ehrb. Cleve's specimens are cer- 

 tainly without processes, and Schmidt figures the valve with no indi- 

 cation of their scars, though in his text he incorrectly says that these 

 scars exist. Processes are also absent from A. apedicellatus sp. n. 

 and abnormal forms of A. Kittoni. 



Habitat : Mors deposit, Jutland (Schmidt, Cleve !). 



2 b 2 



