GYROSIGMA. 



[ 302 ] 



GYROSIGMA. 



Most of the species are found in salt or 

 brackish water; a few are aquatic. They 

 often abound upon the surface of mud. 

 Conjugation or the formation of sporangia 

 has not been observed. The frustules are 

 sometimes found enveloped in amorphous 

 mucus, and those of one species have been 

 found within gelatinous tubes. 



Many species have been described, of 

 which those that have been used as Test- 

 objects will be enumerated. We must, 

 however, express our belief that they cannot 

 truly be regarded as distinct species, unless 

 of microscopic objects, if the term may be 

 permitted. The measurements are mostly 

 those of the Rev. Mr. Smith and Mr. Beck, 

 with which our own have coincided as nearly 

 as could be expected. The species are 

 arranged according to the fineness of the 

 markings, which coincides with the difficulty 

 with which they are detected and resolved 

 into dots ; and the appended figures express 

 the number of striae or rows of dots in 

 1-1000". 



Strice oblique (dots alternate or quin- 

 cuncial, PL 11. fig. 40). 



G. formosum (PI. 11. fig. 25). Broadly 

 linear, attenuated towards the ends ; sig- 

 moidure evident; keel oblique; length 1-60"; 

 striae 36. Marine. 



G. decorum (PI. 11. fig. 26). Rhomboid- 

 linear; attenuated; sigmoidure very evident; 

 keel obhque ; length 1-90"; striae 36. Marine. 



G.speciosum (fig. 28). Linear-lanceolate; 

 sigmoidure resulting from the curvature of 

 one margin of each half of the valve, the 

 opposite margin of each respective half being 

 nearly straight; keel in each half forming two 

 curves, very oblique near the end; length 

 1-90"; marine; striae 44. The halves of 

 the valves resemble the blade of a pocket- 

 knife. 



G. strigosum (fig. 29). Linear-lanceolate, 

 ends rather obtuse, sigmoidure slight ; keel 

 nearly straight in the middle, curved near 

 the ends; length 1-90"; striae 45. Marine. 

 Fig. 40 represents the striae resolved into 

 dots. 



G. quadratum (fig. 34). Rhomboidal, 

 acuminate at the ends ; sigmoidure evident 

 towards the ends ; keel curved, nearly me- 

 dian; length 1-150"; marine; striae 45. 



G. elongatum{V\. 11. fig. 31, and PI. 1. fig. 

 18). Linear-lanceolate, acuminate ; sigmoid- 

 ure slight, uniform; keel median; length 

 1-80"; marine; striae 48. 



G. rigidum (fig. 30). Linear-lanceolate, 



obtuse at the ends ; sigmoidure slight ; keel 

 nearly median; length 1-70"; marine; striae 

 48. 



G. angulatum {Navicula angulata) (PI. 11. 

 fig. 33). Rhomboid-lanceolate or angular- 

 lanceolate ; sigmoidure evident ; keel nearly 

 median; length 1-110"; marine; striae 52. 

 PL 1. fig. 16 represents a valve with the striae 

 resolved into dots; PL 11. fig. 41 represents 

 the dots more highly magnified. 



PL 11. fig. 33 a represents a specimen with 

 the endochrome and nucleus. 



/3 (fig. 33 6). Simply and narrowly lan- 

 ceolate, ends acute. 



y (fig. 33 c). Ends beaked, abruptly 

 flexed. 



G. (Bstuarii (fig. 35). Lanceolate ; ends 

 abruptly tapering, short and beak-like ; sig- 

 moidure evident ; keel not median ; length 

 1-250"; marine; striae 54. 



G. intermedium (fig. 36). Narrowly linear- 

 lanceolate, acute; sigmoidure none, or merely 

 indicated by a slight inequality in the oppo- 

 site margins of the valves; keel nearly 

 straight and almost median; length 1-140"; 

 marine ; striae 55. 



^ G. nubecula. Ends obtuse ; slightly 

 more lanceolate, and shorter ; marine ; 

 striae 55. 



G. delicatulum (fig. 32). Very narrowly 

 linear-lanceolate ; sigmoidure evident ; keel 

 nearly central; marine; length 1-130"; 

 striae 64. 



G. obscurum (fig. 27). Linear, attenuated 

 near the ends ; sigmoidure slight, principally 

 arising from the cm-vature of one margin of 

 each half of the valve; keel not median, 

 especially near the ends ; marine ; length 

 1-200"; stri^ 75. 



StricB longitudinal and transverse (dots 

 opposite, PL 11. figs. 39, 42). 



In most of the following species or forms 

 the dots are not equidistant in the longitu- 

 dinal and transverse rows. 



G. strigilis (fig. 12). Linear-lanceolate ; 

 sigmoidure evident; keel nearly median, 

 flexure double ; marine ; length 1-75 ; striae : 

 longitudinal 40, transverse 36. 



G. balticum (fig. 10). Broadly linear, 

 narrowed at the ends ; sigmoidure apparent 

 at the ends only, and produced princi])ally 

 by the curvature of one margin only ; keel 

 not median, flexure double ; marine ; length 

 1-80" ; striae, both sets, 38. Fig. 39, piece 

 of valve, showing dots. 



jS. Gradually tapering towards the ends ; 

 striae obscure. 



