800 SUMMAEY OF CURRENT RESEABCHES RELATING TO 



Longitudinal Transverse 



Striae per mm. Striae per mm. 



Navicula viridis Kz 2400 .. .. 720 



„ divergens Sm „ (irreg.) .. 1100 



„ divergens Sm. var. .. .. „ ,. .. ,, 



„ stauroneiformis Sm „ .. .. 1200 



„ stauroneiformis Sm. var. latialis „ ., .. 1900 



„ crassinervis Breb. .. .. „ .. .. 1400 



„ rhomhoides :Ehh 1700 .. .. 2400 



Frustulia saxonica B-Sibh. 3600 .. .. 3400 



Scoliopleura convexa Ginn. .. .. 3600 ., .. 700 



„ tumida (Breb.) Eabb. .. „ .. .. 1300 



Pleurosigma halticum ^m. „ .. ., 1450 



„ attenuatiim Sm 1050 .. .. 1400 



„ hippocampus ^va „ .. .. 1750 



„ formosum Sm 1580 .. .. 1900 



„ angulatum Sm. .. ,. „ .. .. 2080 



DoMHn?a reef a (Donk.) Ealfs .. .. „ .. .. 2100 



Toxonidea insignis Tiovik „ .. .. 2250 



Pleurostaurum javanicum Grun. .. 1300 .. .. 1320 



„ acutum Eabh. var. .. 900 ,. .. 1300 



Endostaurum crucigerum (Sm.) Breb. . „ .. .. 1400 



Mr. F. Kitton makes the following observations on the preceding 

 paper : — " If I understand the author aright, it would seem that it is 

 only when dealing with a series of valves produced by a single germ or 

 sporangial frustule that the striation is constant and that the varia- 

 tion never exceeds i in the same species from a different stock. If 

 this means a difference in the number of strise, the variation is con- 

 siderable, e. g. it gives a range in Navicula crassinervis of 11-14 

 in • 01 mm. = 27-35 in • 001 inch. Some error must have been made 

 in the measurement of the transverse striae on the above-named 

 species; the author says they are 14 in the '01 of a mm. (35 in 

 •001 of an inch), only 2 more than those on N. stauroneiformis Sm., 

 and 10 less than those on N. rhomboides, which he says are 24 in 

 •01 mm., a much easier form to resolve than the form called N. crassi- 

 nervis. N. limosa is said to have 19 in *01 mm., but they are easily 

 resolved with an old Ross ^ objective (75°). Endostaurum crucigerum 

 is also stated to have 14 striee in • 01 mm. ; any ^ objective easily 

 resolves both the longitudinal and transverse strife at the same time. 

 Nitzschia sigmoidea Sm., the author says, has 10*75 in •Ol mm.; 

 Smith states them to be 85 (= 34 in •Ol mm.); Sullivant and 

 Wormeley 70 in • 001 of an inch. Professor E. W. Morley * makes 

 them 63 (which is, we believe, accurate). Nitzschia spectahilis ( = 

 Synedra spectahilis of Ehrenberg, and N. sigmoidea (3 of Smith), is 

 stated to have stri© as close as 27 • 50 in • 01 mm. ( = 68 • 75 in • 001 

 of an inch). Smith says they are 42 in •OOl inch ; we make them 

 35 to 38, an average of 14*6 in -01 of a mm. N. amphioxys Smith, 

 20 in • 01 mm. Castracane ; 15 in • 01 mm. Morley. The measure- 



* Mon. Micr. Jouru., xv. (1876) p. 227. 



