32 



HARDWICKE'S SCIENCE-GOSSIP. 



NOTES ON RHIZOSELEXIA SHRUB SO LIE 



RIIIZOSELENIA is a genus (though doubtful 

 by some authors) of tJie family of Diatomacea". 

 They arc found both living and fossil, and though de- 

 scribed by Ehrenberg some forty years ago, are as 

 yet but little known, and as little understood by the 

 general microscopist. 



In a former volume of Science-Gossip, two 

 species of this genus have been described and 

 figured, and further information upon the subject is 

 invited. I therefore offer the result of my observations 

 upon this new species with greater willingness. 



The genus has been made to include several species, 

 »o which Professor P. T. Cleve, of the Royal Swedish 

 Academy of Sciences, seems to be making additions, 

 all of which are interesting, peculiar and beautiful ; 

 while some from the .\ustralian waters are exquisitely 



in consequence of the many important discoveries 

 brought to notice by its discoverer, he has named it 

 " Shrubsolii." 



Shrubsolii is one of the minute species of the genus, 

 and may be described as a long, slender, cylindrical 

 tube, made up of sections (lorica) terminated at each 

 extremity by a beak, or tooth, as its name implies, 

 furnished with pocket-like impressions, and upon the 

 opposite surface with a groove, adapted for the recep- 

 tion of the beak, by which arrangement any number 

 of frustules may be united into a continuous series of 

 indefinite length. The cell contents do not appear to 

 pass from frustule to frustule, so that each individual 

 has an independent existence, though possibly depen- 

 dent upon each other for the performance of certain 

 functions in their union representing the conjugation 

 of some other forms of unicellular organisms (fig. 21). 

 The frustule consists of three parts, an inner, 

 structureless membrane (primordial utricle), C ; an 



Fig. 21. — .A". Slinibsolii by direct, traBsmitted rays united, and with endochrome, X 400.' 



Fig. 22. — The Lorica, X Soo. 



Fig. 23.— With slightly oblique light, X 800. 



Fi^s. 24, 25, 26. — Wiih ceiitr.d stop to acliro condenser, X 650. 



Fig. 27. — Single frustule, with zigzag line, X 400. 



elegant, and may form the subject of a future 

 note. 



In the month of August, last year, \V. H, Shrub- 

 sole, Esq., F.G.S., while making a boating excursion 

 off the Island of Sheppy for the purposes of discovery, 

 suddenly came upon a green, slimy substance, which 

 was covering the surface of the sea, apparently as far 

 as the eye could reach, which soon filled a net he 

 was towing from the stern of his boat, and which, on 

 examination at home, proved to be Rhizoselenia. 

 The proper habitat of this great rarity in the British 

 seas is that part of th.e Atlantic Ocean between 

 Iceland and Greenland ; its presence here, therefore, 

 occasioned some interest. On a further examination 

 by Cleve, that gentleman made a communication to 

 the Royal Swedish Academy, and in his elaborate 

 and valuable work on " New and little-known 

 Diatoms," has offered reasons for regarding this 

 subject as a new and distinct species, characterised 

 by the course of pitnctata, composed strice, and. 



intermediate inorganic, silicious coat, B ; and an 

 external organic corpuscular layer, A. 



The contents of those with which I have been 

 favoured, some in alcohol, and others (with other 

 diatoms) in the water in which they were living, is 

 cellular, of a grass-green colour, imbedded in a gela- 

 tinous, sheath-like, coagulable base, separated from 

 the original homogeneous, pellicular nitrogenous layer 

 (protoplasm). Very occasionally, however, this 

 granular matter is found free in the liquid contents 

 filling the frustule (fig. 21). 



The form and arrangement of the punctata in the 

 silicious deposit is determined by the exteriul 

 organic membrane, the corpuscles, or cells, of which 

 membrane are supported by the inflexible layer of 

 silex. 



The direction of the stri?e is oblique, and con- 

 tinuous, only to the extent of each section (lorica). 

 There are often, therefore, many irregularities (fig. 22). 



A zigzag line traverses the entire length of the 



