134 THE VOYAGE OF H.M.S. CHALLENGER 



Asteromphalus challengerensis, n. sp. (Plate V. fig. 2.) 



Forma rotunda ; lineis umbilicalibus tribus a centro dimanantibus, hinc bipartitis vel 

 tripartitis ; linear umbilicales rectce ; segmentorum vertices obtuso-rotundati ; area radii 

 obsoleti fere obliterata. In mari glaciali Antarctico. 



This round Diatom bears a star with eight radii apart from the obsolete radius. The 

 umbilical lines are three in number, start from the central point, and afterwards subdivide. 

 The vertices of the segments are obtusely rounded, and the central area of the obliterated 

 radius has vanished. 



Asteromphalus challengerensis (?), n. sp. (Plate IX. fig. 2.) 



Forma monstrosa. In mari glaciali Antarctico. 



The frustule here represented is exceedingly instructive and interesting. It is evi- 

 dently a monstrous form, and doubtless originates from the coalescence and simultaneous 

 development of two germs which have combined to form a single frustule. Although 

 similar teratological phenomena frequently occur in the fruits of phanerogams, I have not 

 met with an example hitherto among Diatoms, nor am I aware of its having been observed 

 by others. Although the precise specific determination of such an abnormality is a matter 

 of considerable difficulty, no doubt can exist as to the generic name, inasmuch as an 

 obsolete radius is present, and at once determines it to be an Asteromphalus. Moreover, 

 from the rounded form of the granulated segments, the linear outlines of the radial areas, 

 the locality in which it was procured, and its association with other frustules of the same 

 genus, it can hardly be doubted that we have here to deal with a specimen of Asterom- 

 phalus challengerensis. 



It is to be noted that, while we are here brought face to face with the development 

 of a double germ or double sporule, the two germs, though the products of the same parent, 

 possess different characters, so that the one would apparently have given rise to a frustule 

 with a smaller number of radii than the other. If this be admitted, then it is clear that 

 no importance should be placed on the number of radii in specific determinations. 



Asteromphalus wyvillii, n. sp. (Plate V. fig. 6.) 



E maximis ; radiis prseter obsoletum viginti sex, intra marginem terminantibus den- 

 ticulo signatis ; areas granulatse intrarnarginales ad verticem truncata? ; linese umbilicales 

 ab area radii medii circumradiantes, simpbces vel semel et bis dichotomse, et medio 

 dupliciter curvatse. Diametrum arese centralis 65 /*, valvse 226 m. In mari Pacifico. 



This is without doubt the most singular and superb specimen of the genus Asterom- 

 phalus which has up till now been recorded. Its immense size ( = 226 n in diameter), 

 the great number of its radii, and the relative smallness of the central disc of the star 

 are remarkable. From the outline of the central area of the obsolete radius proceed many 



