44 W. M. BALE ON SOME OF THE DISCOID DIATOMS. 



from the umbilicus and join the sub-marginal zone without any 

 interruption of the structure, which indeed is similar all over the 

 valve, except the narrow hyaline border. The valve is very thin, 

 covered with very delicate striae, crossing each other obliquely, 

 and most easily seen on the narrow rays. The secondary 

 markings consist of a fine, delicate, irregular reticulation, at the 

 angles of which are dark points or apiculi, which are larger and 

 darker on the narrow rays and sometimes round the inner border. 

 On each of the linear rays, near the border, is a minute process. 

 In Grunow's figure both the cuneate areas and the dividing rays 

 are abruptly truncate at the border, but my specimens do not 

 agree with this, as the narrow rays widen out in a regular curve 

 towards the border zone, with which they are continuous, the 

 cuneate areas having of course their outer corners rounded off 

 correspondingly, while they do not quite reach the border. Owing 

 to the thinness of the valve, however, and the depressions being 

 by no means abrupt at the outer ends, this character might often 

 pass unnoticed, unless the valve happens to be lying obliquely, 

 when it becomes more conspicuous. Possibly my specimens, which 

 were found in recent gatherings from Port Phillip, may differ 

 specifically from Grunow's guano specimens, but the late 

 Mr. Comber considered them the same. 



I think the characters by which this species is distinguished 

 from all others of the genus are such as to entitle it to at least 

 the rank of a sub-genus, for which I would suggest the name 

 Radiodiscus. It is possible, however, that it may be brought 

 under the genus Actinodictyon Pantocsek, but I am uncertain 

 of the affinities of that genus, of which I have seen no specimens. 



I have a single valve, apparently belonging to A. hispidus, 

 which differs in several respects from the usual form. Its 

 depressions are extremely slight, there are no secondary markings 

 and no apiculi, and the cuneate areas terminate in a hyaline 

 band, as in A. splendens, etc.; it also has exceedingly narrow 

 lines (pseudo-raphes) on the narrow areas ; the border is wanting. 

 It may be a varietal form, or possibly an internal disc, but its 

 pseudo-raphes and hyaline bands seem to indicate a closer affinity 

 with such forms as A. adriaticus than would be inferred from the 

 typical form. 



Journ. Quckett Microscopical Club, Ser. 2, Vol. XII., No. 72, April 1913. 



