DIATOM ACE JE 



-FAMILY ACHNAXTHE.E. 



305 



pletely. Another Family in which there is a dissimilarity in the 

 two lateral surfaces, is that of Achnanthece; the frustules of which 

 are remarkable for the bend they show in the direction of their 

 length, often more conspicuously than in the example here repre- 

 sented. This family contains free, adherent, and stipitate forms; 

 one of the most common of the latter being the Achnanthes 



Fig. 139. 



Gompkenemagemmaturti : its frustules connected by a dichotomous stipes. 



longipes (Fig. 138), which is often found growing on Marine Alga. 

 The difference between the markings of the upper and lower valves 

 is here distinctly seen ; for while both are traversed by stria, which 

 are resolvable under a sufficient power into rows of dots, as well as 

 by a longitudinal line, which sometimes has a nodule at each end 



