Structure of girdle 



85 



bands occurs in Rhizosolenia, in which genus the girdle view is the normal 

 aspect presented by the diatom. In fact, the great elongation of the girdle 

 renders it almost impossible to obtain a view of the valve-face because 

 the diatom will not rest on that face. Similar elongated girdles occur in 

 the genera Guinardia, Attheya, Peragallia, and other centric diatoms. 



The girdle is also complex in the freshwater Eupodiscus lacustris described 

 by Wille ('03) from the Zambesi, and in some of the naviculoid diatoms, such 

 as Stauroneis Biblos Cleve ('92). Intercalary bands arise during the process 

 of cell-division, being formed immediately after the new valves, the con- 

 necting band being the last-formed segment of the new half-cell. Like the 



v- 



i.b. fc. wmj 

 \ 



t.v. 



ll. 



v. 



v 



Fig. 58. A, section of edge of valve of Epit hernia turc/ida (Ehrenb.) Kiitz. to show attachment 

 of connecting band (c.b.), intercalary band (i.b.) and valve (v). B, similar section of Clima- 

 cosphenin moniligera Ehrenb. C, longitudinal section of the half-cell of Grammatophora 

 maxima Grun. showing the intercalary valve (i.v.), which is an intercalary band furnished 

 with a longitudinal septum (s.). D, single cell of Mastogloia Smithii Thwaites, disjointed so 

 as to show the two valves, two intercalary valves, and two connecting bands. E, half-cell 

 of Rhizosolenia stylij'ormis Brightw., showing valve, connecting baud, and intervening 

 intercalary bands. F and G, girdle and valve views respectively of Guinardia flaccida 

 (Castr.) Perag. </., the two connecting-bands forming the girdle; i.b., the numerous inter- 

 calary bands. (A, I), C and E, after 0. Miiller ; D, after W. Smith; F and G, after Van 

 Heurck.) 



connecting bands, the intercalary bands are in many cases but imperfectly 

 closed hoops. The openings in adjacent bands, however, are not in the same 

 line, and are invariably covered by some portion of a neighbouring band. The 

 valves, connecting bands, and intercalary bands fit against one another by 

 bevelled and generally curved edges (consult fig. 58 A C), but the con- 

 nection is in some cases much looser than in others. 



Some diatoms possess longitudinal septa, which are invariably ingrowths 

 from the intercalary bands. Such septa are always more or less considerably 



