A FOSSIL MARINE DIATOMACEOUS DEPOSIT. 139 



Aulacodiscus janischii, n. sp., Gr. and St. — This species has been 

 hitherto considered by us as A. stoschii, Jan. The first forms 

 observed were smaller than those which have occurred in samples 

 of the material obtained since, and closely resembled the figure of 

 A. stoschii in Messrs. Walker and Chase's work referred to by us 

 (supra, p. 8). Herr Janisch has, however, kindly allowed us to 

 examine an original example of his form, and we find that the 

 Oam aru species differs entirely. We have much pleasure in naming 

 this fine Diatom after one who has done so much in furtherance of 

 the knowledge of the Diatom acea3. 



Valve large, with moderately convex centre, from which extend 

 seven bullate expansions, ceasing close to the margin; from the 

 ends of which project the small cylindrical processes. 



Between each expansion there is usually an undulation which is 

 very conspicuous in the larger examples. The furrows are very dis- 

 tinct at the processes, but as they approach the centre are gradually 

 lost on the rough granular surface of the valve, which is covered 

 with crowded radiating lines of dots. 



Diam. to -02". (PI. XI, Fig. 28.) (A small example). 



A.janischu, var. abrupta. — This form has usually six processes. 

 The convex centre does not branch into the bullate expansions as 

 in the type form, but they rise from its edge and terminate abruptly 

 on the margin. They are broader at the ends, and more con- 

 spicuous than in the type. Diam. to '005". 



Note. — This form approaches very nearly to A. mammosus, Grev. 

 (" T. M. S.," Vol. xi, p. 70), of which it may be a six-processed 

 form. 



A. rattrayii, n. sp., Gr. and St. — We at first considered this 

 species as one of the forms of A.beeveria?, Johns., but further examina- 

 tion and comparison with an authentic specimen of that rare form 

 in the possession of our friend, F. Kitton, Esq., have convinced 

 us that it is distinct. We have much pleasure in naming it after 

 the well-known diatomist, Mr. R. Rattray, of Dundee, who has 

 assisted us so materially in the examination of this deposit. 



Valve convex, with flattened margin and striated rim. Processes 



usually three, small, oval, considerably within the margin. Cellules 



hexagonal, about 10 in -001", strongly papillate, closely covering 



the surface in radiating lines, with the exception of a small irregular 



clear umbilicus. Scattered spines occur giving the surface a 



scabrous appearance, especially near the margin. Furrows formed 



