KETOKT ON THE DIATOMACE.E. 



79 



This Diatom was obtained in a surface collection made in the Antarctic Ocean between 

 Kerguelen and Heard Islands. The frustules are subquadrate, and arranged in a series. 

 The valves are oval, the one being convex and the other flat. The setae originate in 

 the centre of the valve, and, after curving round each other, diverge horizontally. In 

 the figure only two awns are seen between two adjoining frustules, the remaining two 

 beinc; either broken off or shortened. On the terminal valve the setae are seen in an 

 embryonic form as a pair of short protuberances. At their origin they are always 

 convolute, a characteristic which is referred to in the name of the species. 



Chsetoceros radiculum, n. sp. 



Frustulum solitarium ; valvis ovatis, bino processu submarginali, inflato, costulato, 

 brevi. Ad meridiem insulae Heard. 



This very puzzling form was collected to the south of Heard Island in the Antarctic 

 Ocean. It is always solitary, and its setae, instead of extending in a long line, form 

 short swollen appendices, like bulbous roots, which are to a greater or less extent marked 

 by longitudinally directed costae that sometimes have their origin on the plane of the 

 valve. To increase the difficulty of fully understanding this type it is to be noted that 

 in addition to two setae or cornua of the form just described there are in some cases 



Ch&toceros radicu- 

 lum, d. sp. 



Chcctoccros radiculum, n. sp., rar. a. 



Chatoceros radiculum, n. sp.. 

 var. /3. 



protuberances, which are twice as long, but are provided with less pronounced swellings, 

 and are devoid of costae. Such forms may be provisionally characterised as constituting 

 variety a of the typical species. In a second group — variety /8 — there is found a trans- 

 versely striated median zone and a single median projecting knob between each pair of large 

 bulb-like marginal protuberances. Whether these differences from the typical species are 

 to be regarded as varietal or as indicative of so many distinct species it is difficult 

 to decide, although probably the former view is the more correct, and has been here 

 adopted. 



