242 



AMPHIPLEURA. 



dots, arranged in regular longitudinal rows, 12 in 1 c.d.m., flexed in the 

 middle. Length, 4-5 c.d.m. Breadth, 2 c.d.m. 



Marine. South Coast of England (Roper.). 



GENUS 14. AMPHIPLEURA KUTZ., 1844. 



Frustules fusiform. Valves narrowly lanceolate, 

 furnished near each edge with a marginal keel. 

 Central nodule obsolete ; the two terminal nodules 

 very elongate. 



The genus Amphiplcura has for a long time been 

 noted as a microscopical test of extreme difficulty, and, 

 until the invention of homogenous objectives, the trans- 

 verse striae could not be seen without the assistance of 

 some extraordinary objectives, such as the i-6th of Tolles, 

 and then it was necessary to employ monochromatic illu- 

 mination. It was only in 1884, by employing a prepara- 

 tion of silvered Amphipkura, that I was able to resolve 

 and photograph this diatom under a silvered aspect. 



Fig. 42. Amphiplcura . ,. , , 



fellucida. This resolution was for a long time disputed, and as 



other microscopists were unable to obtain the same resolution, it was thought 

 that I was the victim of an optical illusion. The discovery of the arsenical 

 medium, the 2-4 of Prof. Smith, and especially the construction of the famous 

 objective with an aperture of r6o, which Messrs. Zeiss placed at my disposal 

 in 1889, enabled me in that year to publish an irreproachable photograph of 

 the Amphipkura resolved into beads, and that put an end to all further dis- 

 cussion on the subject. 



The genus Amphipkura includes four or five well-established species, only 

 one of which, and that the most delicate, lives in our regions. The Amphi- 

 pkura Lindheimeri, the most beautiful and largest species, inhabits America, 

 but a variety M Lindheimeri var. Truanii H.V.H.), has been found in 

 Spain. 



A. pellucida KiitZ. (Bac, p. 103, pi. 3, f. 52, and pi. 30, f. 84 ; 

 H.V.H. Atl., pi. 17, f. 14, 15 and A*; Type No. 165), plate 5, fig. 253. 



Valve narrowly lanceolate, with acute apices. Raphe not interrupted 

 in the median portion of the valve. Central nodule very rudimentary ; 



