REPORT ON THE DIATOMACE.E. 55 



In fig. S the frustules are simple and singularly slender, and the borders are provided with 

 fine but very salient points — spines or thorns — which at the superior extremity assume 

 the appearance of two apiculi. The frustules are never in groups of more than eight, and 

 the angles included between any adjoining pair are approximately equal, with the excep- 

 tion of that which corresponds to the opening of the armilla, which is always somewhat 

 larger. 



This also applies to the frustules shown in fig. 7, which differ from the last only in 

 bein^ double, an appearance which has been caused by the temnogenetic changes which 

 have tak^n place. Sometimes promiscuous groups of double or simple frustules are to be 

 met with, but much more frequently, after division has occurred, the armilla, in which 

 the inferior extremities of the frustules are planted, breaks up by separation of the double 

 frustules, a result which is probably brought about by the development and swelling of 

 a triangular isthmus, which unites the superior extremities. In the course of this curious 

 change in the position of the locus of union the frustules are frequently found to be 

 simply united in short zig-zag series. 



Thalassiothrix curvata, n. sp. (Plate XXIV. fig. G. ) 



Frustulis linearibus, subcurvatis, crasiusculis, radiatim vel alterne pulvinulo conjunctis; 

 punctulis frustulorum marginalibus duplo quam in Thalassiothrice frauenfeldii rarioribus. 

 In mari Japonico. 



In this figure no traces of the small connecting cushions are to be found, as these have 

 been removed during the process of incineration. The frustules are bacillar, and flanked 

 on each side by a line of small points resembling those which are found in the above 

 described Grunowian species, but they are slightly curved, much shorter and wider, and 

 the punctations are only half as abundant as in Thalassiothrix frauenfeldii. 



From such considerations the specific value of this Diatom cannot be doubted, especially 

 as it occurs in sreat abundance in some collections. 



Fragilaria (Lyngb.), Agardh. 



It has already been indicated that the enormous glaciers which cover the mountains 

 of polar lands, and which ultimately reach the ocean and form icebergs, are the means of 

 transporting freshwater Diatoms into the sea, where these organisms float freely when the 

 ice has been melted. Frustules of Asterionella formosa, Hass., Ceratoneis arcus, Kg., and 

 various species of the genus Eunotia, wdiich is not only peculiar to fresh water, but which 

 only vegetates at an elevation of several hundred feet above the level of the sea, have 

 been thus transported, 1 and the same phenomenon has taken place in the case of the genus 

 Fragilaria, of which some new species must now be recorded. 



1 Confer., p. 50. 





