

1891.] Rocky Mountain Rhizopods. 1073 
chitinoid matter is normally very slight, and this particular 
Difflugia is an interesting exception. 
Quadrula symmetrica Schulze.—I have found this beautiful 
species abundantly in most of my gatherings, but mostly repre- 
sented by very small-sized individuals (length 0.040-0.060 mm.). 
On the contrary, in one single locality the species was to be 
found under what might be called a giant form (length 0.100- 
0.150 mm.), which presented this other peculiarity, that the square 
plates composing the shell, instead of being disposed, as in the 
typical form, in a high degree of symmetry, showed great dis- 
order in their arrangement, and very often overlapped each other. 
The sides of the shell, instead of looking like a tolerably con- 
tinuous curve, appeared like a series of broken short lines. 
These two varieties, if they must be considered as such (in my 
opinion, they are more than varieties), were very sharply distinct, 
and I have not seen any transitional forms. 
Nebela collaris Leidy.—This species also was represented at 
Caribou by two very distinct forms: first the typical one (forma 
genuina Taranck), not very abundant asa rule, and totally absent 
in some places; then another form, or dwarf variety, extremely 
abundant, and often to be found quite alone in some localities. 
This latter form agrees perfectly with a variety which Leidy has 
figured in his great treatise (Pl. xxu., Figs. 11, 12, 16). 3 
Nebela longicollis Penard—Rather abundant in nearly all my 
gatherings. The speciesis very different from the preceding ; yet 
the form I found at Caribou could hardly be referred to the 
Nedela longice ollis such as I described it in 1890* (which appears 
to be the same as Wed. barbata—Leidy, Pl. xxiv., Figs. 14-17). 
It agrees, on the contrary, very well with two shells figured by 
Leidy (Pl. xxiv., Figs. 18, 19) as “ intermediate in character to 
Neb, barbata and Neb. collaris,’ and at the same time shows rela- 
tions to the form that I called /ageniformis. I mention here the 
` Caribou form under the name dongicollis, being of opinion that 
Neb. barbata and the two Figs. 18 and 19 of Leidy refer to one 
2 Etudes sur les Rhizopodes d'eau douce. Mémoires de la Société de Physique et 
d'Histoire naturelle de Genéve, 1890. All the species mentioned in this paper, and 
which bear my name, have been described in the same w 
Am. Nat,—December.—3., 

