G. C. KAROP ON WHAT WAS THE AMICTAN TEST? 81 



In a paper by Mr. J. Newton Torakins " On Resolution of 

 Diatoms by Double Prism Illumination,"* he speaks of N. rhom- 

 boides as " the Amician test of the London, although, perhaps, 

 not of the American microscopists," a very queer expression 

 unless, indeed, as I suspect, the thing was a variable. Mr. E. G. 

 Lobb, a very well-known microscopist in his day, in a paper 

 entitled " Note on Illuminating Objects with High Powers," 

 (" Trans. Mic. Soc," Lond., N.S. xiv., 1866, pp. 39-41), gives 

 minute directions for using a condenser of 170° (Powell's) in 

 resolving tests, stating the apertures and stops suitable for quite 

 a number of diatoms. He says : " To examine N. cusjridata, N. 

 rhomboides, P. fasciola, P. macrum, etc., use No. 11 aperture 

 and stop No. 2, which will require a slight alteration in position 

 only, when the checks will appear distinctly. For the Amician 

 test use the slots instead of No. 2 stop." From this it seems 

 quite clear that Mr. Lobb's Amician test, at all events, was not 

 N. rhomboides. 



In the first three editions of the " Micrographic Dictionary," 

 viz., 1856, 1860 and 1875, Amici's test is given as N. gracilis, 

 Ehr., which Smith, " Syn.," p. 75, refers, with a query, to his 

 Pinnularia gracilis. From the figure it appears to me very un- 

 likely. In the latest edition of the Dictionary, 1883, sub voce 

 Test Objects is given, " N. affinis, Amici's test object, that used 

 at the Exhibition of 1862, mounted in balsam, the transverse 

 lines. "t Mr. Ingpen thinks this would now be considered a form 

 of rhomboides, but both Van Heurck and Brun make it allied to 

 N. pi'oducta, W. S. It is evidently a variable species, but I 

 think the striation is coarser than any ordinary rhomboides ; more- 

 over, it is figured with the central and terminal nodules of a true 

 Navicula. 



I have a, more or less, distinct recollection of a Grammatophora, 

 probably subtillisima, being given as the Amician test ; possibly 

 this is the American variant. 



* When and where this paper was published I have been unable to find, 

 but it is quoted at some length in the Sixth Edition of Hogg, " The 

 M croscope," etc., 1867, pp. 175-8, and Eev. J. B. Eeade somewhere mentions 

 that Tomkins used a double prism illumination in 1861. 



t Navicula affinis, sous le nom de Test d'Amici a ete' employee d'apres le 

 Prof. Yan Heurck a l'exposition de Londres a 1862 pour juger les Micro- 

 scopes. Robin, "Traite du Micros, et des inject.," 1877, p. 312. 



