2 6o DISCOVERY REPORTS 



senarius" "synonym Actinocyclus senarius 1838". (Ehrenberg 1840(2, p. 137, pi. 4, 

 fig. 1 a-e.) 



In subsequent work, Ehrenberg (1854, pi. 19, fig. 11, pi. 21, fig. 8) consistently re- 

 ferred Actinocyclus senarius 1838 to the genus Actinoptychus 1843, p. 400, but retained 

 Actinocyclus octonarius (1838, p. 172, pi. 21, fig. 7) as the type species of the genus 

 Actinocyclus. 



Examination of figs. 6 and 7 on pi. 21 (1838) might lead one to suppose that the 

 organisms illustrated are congeneric, and the descriptions provided do not reveal any 

 difference between the two species except in the number of internal rays. But in view 

 of the definite way in which Ehrenberg separated Actinocyclus senarius to form the type 

 species of the new genus Actinoptychus (1843, p. 400) and the improved illustrations 

 of Actinocyclus octonarius provided in the Mikrogeologie (1854, pi. 21, fig. 11, and 

 particularly pi. 22, fig. 14), it is clear that this is not so. The apparent similarity between 

 figs. 6 and 7 on pi. 21 (1838) must be explained as the result of a lack of intimate know- 

 ledge of the characters which Ehrenberg himself subsequently emphasized as the chief 

 differences between the two genera. The confusion arose in the first place because 

 Ehrenberg placed the same interpretation upon the furrows on the valve of Actinoptychus 

 as upon the interfascicular spaces on the valves of Actinocyclus. 



Actinocyclus bifrons Karsten. 

 Karsten, 1905, p. 92, pi. 9, fig. 8. 



Cells discoid, solitary, valves dissimilar. Upper valve slightly convex, usually 

 flattened at the centre, surrounded by a very narrow radially striate margin. Valve sur- 

 face covered with puncta. Puncta irregularly arranged towards the central area of the 

 valve, often obscurely concentric. In the peripheral area the puncta are arranged in 

 fascicules of parallel lines, lines parallel to the first or radial line of each fascicule. 

 Pseudo-ocellus small, inconspicuous, marginal. The lower valve is more deeply convex, 

 and is surrounded by a broad radially striate margin, the striate portion bounded by a 

 narrow hyaline margin. The valvar portion is covered with moniliform striae, striae in 

 fascicules of parallel lines in the peripheral area, but somewhat sparse and irregularly 

 arranged in the central area. A small pseudo-ocellus present upon the striate margin, 

 not connected with the valvar portion ; pseudo-ocellus globiform. Chromatophores : 

 numerous small cocciform bodies, often conglomerated. Diameter of valves 70-90^. 



A typical Antarctic species, neritic, probably spending some of its time as a bottom 

 form. Common around the South Sandwich Islands and South Georgia. 



Observed at Sts. 368, 369, 378, 379, 380, 381, 382, 384, 475, 477, 478, 508, 510, 576. 



Actinocyclus complanatus Castracane. 

 Castracane, 1886, p. 145, pi. 4, fig. 9. 

 Cells discoid, valves almost flat, slightly convex at the margin. Valves covered with a 

 fine areolation arranged in radiating fascicules of parallel lines. Areoles entire over the 

 whole surface ; central hyaline area absent. Margin complex, consisting of a wide band 



