SYSTEMATIC ACCOUNT 267 



Mann's enforcement of the law of priority in nomenclature had brought any excep- 

 tionally disastrous results, or in fact influenced the literature in any way whatever. There 

 is no question that the genus Hemiptychus was legally and validly described and that the 

 use of Hemiptycha for a genus of insects does not in any respect invalidate it. It must be 

 admitted that Ehrenberg willingly adopted Bailey's suggestion to change the name to 

 Arachnoidiscus, either to avoid the chance of complications arising out of the similarity 

 of the two names, or in deference to some unwritten understanding that existed amongst 

 scientific men of that day. 



The problem is a difficult one, and I feel that if Mann had reaffirmed his establish- 

 ment of Hemiptychus in 1925, his decision would have completely dominated diatom 

 literature of the twentieth century. It is a matter for regret that Mann's withdrawal of 

 Hemiptychus made the conservation of a later name inescapable. 



Arachnoidiscus Ehrenbergii Bailey ex Ehrenberg. 



Ehrenberg, 1849, p. 64. 

 Hustedt, 1929, p. 471, fig. 262. 



Cells discoid, solitary, usually epiphytic. Valves flat or nearly so, slightly raised in the 

 centre. Valve surface almost completely divided into sectors by strong radial furrows. 

 These primary rays penetrate almost to the centre of the valve and are joined upon the 

 inner side by a broad central membrane. Primary rays usually eight to thirty-six. 

 Shorter secondary rays of varying length are arranged radially between the primary 

 ones. A system of short tertiary rays is sometimes observed, particularly in mature 

 frustules. A small central hyaline area present. Covering the valve face, between the 

 rays, is a coarse areolation. Areoles often arranged in pairs, in more or less regular con- 

 centric circles. The ring of markings that surrounds the small central area is usually 

 larger than the others, and the markings themselves are often elongated, rectangular or 

 cuneiform. Areoles over the remainder of the valve are subrectangular in shape. 

 Chromatophores : several large plates. Diameter of valve 140-220/x. 



This species favours tropical and subtropical waters, so it is a matter of great interest 

 to note its occurrence in the Bransfield Strait. Van Heurck (1909) reported A. Ehren- 

 bergii var. indica from the Bellingshausen Sea, south-west of Peter 1st Island. A littoral 

 diatom ; it probably spends part of its time as a bottom form, epiphytic often upon red 

 algae and corallines; sometimes found in large numbers. 



Observed at St. WS481. 



Subfamily ASTEROLAMPROIDEAE 



Genus Asterolampra Ehrenberg 

 Ehrenberg, 1844 



Asterolampra Grevillii (Wallich) Greville. 



Greville, i860, p. 113, pi. 4, fig. 21. 



Hustedt, 1929, p. 489, fig. 274. 



Asteromphalus Grevillii Wallich, i860, p. 47, pi. 2, fig. 15. 



Asterolampra rotula Greville, i860, p. m, pi. 3, fig. 5. 



