REPORT ON THE DIATOMACEiE. 135 



of the umbilical Hues of the twenty-six remaining radii, and among these some remain 

 simple, while others bifurcate once or twice. Almost all the lines have a double curve in 

 the course of their length, and the hyaline radii terminate before arriving at the circum- 

 ference in a salient or denticulate point. The apices of the granulated segments are 

 sharply truncated. 



The specific name of this elegant frustule has been given in honour of the late 

 Professor Sir Wyville Thomson, formerly Director of the Challenger Commission. 



Asteromphalus antarcticus, n. sp. (Plate XVI. fig. 11.) 



Forma rotunda, parva ; dissepimentis cuneatis, ad verticem truncatis ; lineis umbili- 

 calibus rectis ; areis radialibus linearibus et denticulo terminal: instructis. Ad mare 

 Antarcticum. 



This small disc was collected by means of a surface net to the south of Heard Island 

 in the Antarctic Ocean, being found associated with many specimens of Asteromphalus 

 darwinii, Grev. 1 It possesses five radii — apart from the obsolete radius — and the 

 umbibcal fines are straight and proceed from the centre. The radial areas are broadly 

 linear, and each terminates near the margin in a well-defined granule. The areolated 

 segments are bounded by internally concave margins, with the exception of those which 

 flank the obsolete radius, and which pass by an elegant curve into the smooth area in the 

 centre of the disc. The ensemble of such characters must be looked upon as sufficient 

 to constitute a good species. 



Asterolampra, Ehrenb. 



The genus Asterolampra, though bearing a great affinity to certain forms of Asterom- 

 phalus, 2 has been too hastily united with the latter by Greville. 3 It embraces some of the 

 most elegant forms of Diatoms, and has been defined by Ehrenberg, as noted by Pritchard 

 (op. cit., p. 836), in the following manner: — " Frustules simple, disciform; disc orbicular 

 with marginal areolated or punctated compartments, separated by smooth rays which 

 proceed from a hyaline central area ; central area divided by lines which radiate from the 

 umbilicus to the apex of each compartment, compartments and rays symmetrical." The 



1 Micr. Journ., vol. viii. pi. iv. figs. 12 and 13. 



2 This genus was established by Ehrenberg for certain Antarctic Diatoms brought home by Sir Joseph 

 Hooker, and collected during the cruise of H.M.SS. "Erebus" and "Terror," Monatsber. d. k. Alcad. d. Wiss. 

 Berlin, 1844, p. 198. See also Kiitzing, Spec. Alg., 1849; Araer. Journ. Sci. and Art., vol. xxii. p. 1; Ehren- 

 berg Mikroceologie, pL^ xxxv. A closely allied genus, Spatangidium, was proposed by Br^bisson in 1857» 

 Bull, de la Soc. Linn, de Normand., vol. ii. 



• 3 Greville, Descriptions of Diatoms observed in Californian Guano, Micr. Journ., vol. vii. p. 157 ; Greville 

 on the Asterolamprae of the Barbados Deposit, Micr. Journ., n. s., vol. ii. p. 42 ; Wallich on Siliceous Organisms 

 found in the Digestive Cavities of the Salpas, and their relation to the Flint Nodules of the Chalk Formation, 

 Micr. Journ., voL viii. p. 44. 



