108 FRESHWATER RHIZOPODS OF NORTH AMERICA. 



but passing thence they gradually become smaller approaching the edge 

 of the rim or reflected lip. 



Only in the variety with spines to the fundus, previously indicated as 

 D. olla, from the sphagnous ponds of New Jersey, have I seen a few speci- 

 mens in which the shell was composed of colorless chitinoid membrane, 

 incorporated with diatoms and fine sand grains, as seen in fig. 29, pi. XIX. 



The interior sarcode of D. urceolata, in all its variety of forms and in 

 all seasons, I have found to be colorless, independently of the hues given 

 to the central portion of the endosarc by the varied nature of the food. 

 The pseudopods are ordinarily from two or three to half a dozen, and of 

 the usual simple digitate kind. 



Difflugia urceolata by transitional forms merges into D. acuminata. 



DIFFLUGIA CRATERA. 



Plates XII, figs. 19-21 ; XVI, fig. 35. 

 Difflugia cratera. Leidy: Proc. Ac. Nat. Sc. 1877, 307. 



Shell goblet-shape, with oval or spheroidal body and wide cylindroid 

 neck; fundus obtuse; mouth terminal, large, circular, truncating the neck, 

 or with a reflected rim. Composed of colorless chitinoid membrane, incor- 

 porated with minute particles of sand and dirt. 



Size. — Length 0.056' mm. to 0.066 mm.; breadth of body 0.036 mm. 

 to 0.042 mm.; breadth of neck 0.028 mm. to 0.036 mm. 



Locality. — Among Ceratophyllum and other aquatic plants. Canal at 

 Bristol, Berks County, Pennsylvania; Buffalo, New York. 



Difflugia cratera is one of the smallest species of the genus, and, 

 though apparently rare, may be common enough, but have escaped frequent 

 observation from its diminutive size. I first found it among hornwort, col- 

 lected in the canal at Bristol, Pa., August, 1876, and noticed about a dozen 

 individuals. I have since met with it recently, August, 1878, in some 

 sediment from the water-supply of Buffalo, New York. The sediment 

 sent to me, on a glass slip, for examination, consisted mainly of the 

 curious four-spined infusorian, Ceratium longicome, and with it I detected 

 two individuals of Difflugia cratera. All the specimens observed appeared 

 to be empty shells, though it is not improbable some of them may have 

 contained the living sarcode, which, being contracted and transparent, 

 escaped notice. 



