GENUS DIFFLUGIA— DIFFLUGIA ACUMINATA. HI 



urceohzta, and the pyriform varieties into D. pyriformis, while the drop- 

 tube-like forms are the most peculiar or characteristic. 



The shell of Difflug'ia acuminata is ordinarily composed of clear quartz- 

 sand, as in D. pyriformis. Occasionally I have seen particles of garnet 

 mingled with the former, as represented in figs. 14, 15, pi. XIII. Some- 

 times the quartz-sand is mingled with variable proportions of diatoms. 



Not unfrequently the shell is composed of colorless chitinoid membrane, 

 incorporated with quartz-sand alone or with this and intermingled diatoms. 

 In this kind usually the grains of sand are closely placed in juxtaposition at 

 and near the mouth of the shell, but are elsewhere scattered and separated 

 by wide intervals. In some cases, the shell is more or less covered with 

 large diatoms, generally adherent in the length, and diverging upward 

 beyond the boundary of the shell, as seen in figs. 21, 22. 



Certain specimens found among sphagnum consisted entirely of dia- 

 toms, as seen in figs 23-26, in most cases (which is unusual) still retaining 

 portions of the endochrome. 



The sai-code of Difflug'ia acuminata is colorless, excepting the usual 

 coloring in the endosarc dependent on the presence of food, though I 

 have met with an individual, as seen in fig. 15, in which the endosarc was 

 bright green. In this case the color may have been due to the food, as 

 the specimen was obtained from among an abundance of green algae. It 

 should be mentioned, however, in this relation, that most of the specimens 

 from which drawings were made were empty shells, chosen on account of 

 their comparative translucency and distinctness of structure. 



The range of size of Difflug'ia acuminata is considerable. The smallest 

 ones observed are those composed of diatoms, from sphagnum. These are 

 about the -^th of an inch in length by the ~f\\ of an inch in breadth 



One of the smallest amphora-like shells, composed of sand, measured 

 the „J th of an inch long by the ^th of an inch broad. One of the largest 

 amphora-like shells, composed of sand, measured the ^th of an inch long 

 by the jith of an inch broad ; and one of the largest pyriform shells had 

 nearly the same measurement. The largest drop-tube-like shell measured 

 nearly the ith of an inch long by the ^th of an inch in breadth. 



Difflug'ia acuminata is one of the commonest of the genus, and is found 

 almost everywhere with other familiar kinds of Difflugia. It is one of 

 the three forms originally indicated and figured by Leclerc as character- 



