240 UNIVERSITY OF COLORADO STUDIES 



(42) Lecquereusia Schlumberger. Shell globular, with a large neck twisted to one 

 side, as though beginning a spiral, and ending in a round oE>ening through which 

 the pseudopodia protrude. L. spiralis (Ehrenberg). 



(43) Difflugia Leclerc. Shell more or less urn-shaped, composed of foreign matter 

 (mostly sand grains) agglutinated together by a chitinous secretion. One end is 

 rounded (rarely pointed), the other occupied by the broad, round mouth, from 

 which the pseudopodia protrude. Exceptional species are D. constricta, in which 

 the subterminal mouth is lateral, and D. arcula, which is very broad, rounded, 

 patelliform, with the oral opening in the middle of the flat side, and trilobed. 

 D. rubescens has the plasma of a beautiful brick-red color. D. pyriformis is much 

 larger than any of our other species; D. fallax and lucida are extremely small. 

 D. rubescens has the neck more or less constricted, at least in the normal form. 

 D. bacilli/era is a slender species, always more or less covered with diatoms. Our 

 species are D. pyriformis Perty,* D. rubescens Penard (type-locality in Boulder 

 County), D. arcula Leidy, D. lucida Penard, D. fallax Penard, D. bacillifera 

 Penard, and D. constricta (Ehrenberg). 



(44) Nebela Leidy. Shell flask-shaped, compressed, so that the lateral view is 

 only about half as broad as the other; surface areolated, composed of small roimd 

 or oval plates; plasma containing rovmd, bluish grey or yellowish masses. N. 

 collaris (Ehrenberg); N. tubulosa Penard; N. longicollis Penard; N. dentistoma 

 Penard. The species are much alike. N. dentistoma is much broader than the 

 others, with the edges of the mouth more or less crenulate. N. tubulosa is sharp- 

 edged at the aboral end, so that in lateral view this end appears pointed. N. 

 longicollis is relatively slender, little compressed. The last may not be distinct 

 from N. barbata Leidy. 



(45) Quadrulella Cockerell. Shell like Nebela, but composed of relatively large 

 quadrangular plates. In the typical species the globules in the plasma are red. 

 Q. symmetrica (Wallich). In his recently published (1911) paper on the Rhizo- 

 pods of the British Antarctic Expedition, Penard calls attention to the curious 

 fact that while the square plates of Q. symmetrica are siliceous, those of Q. irregu- 

 laris (Archer) are calcareous, and will dissolve in hot concentrated sulphuric acid. 

 He therefore inclines to agree with Awerinzew that the two animals are reaUy 

 generically distinct, and represent a case of convergent evolution. 



(46) Heleopera Leidy. Shell ovoid, much compressed laterally, with a reticulate 

 or alveolar surface. This is very like Nebela, but has sand-grains at the aboral 

 end. The pseudopodia are numerous. Our species is of a wine-red color. H. 

 rosea Penard. 



(47) Centropyxis Stein. Shell discoidal, rarely oboval, sometimes subhemi- 

 spheric, chitinous, more or less covered with foreign particles. Our species has 

 projecting points. C. acideata (Ehrenberg). Penard considers this to show much 

 aflinity with Difflugia constricta, and notes that both are extremely timid, rarely 

 showing their pseudopodia. 



(48) Arcella Ehrenberg. Shell hemispherical or discoid, or {A. costata) with 

 flattened lateral faces; oral surface flattened, more or less concave, with a round 

 opening for the pseudopodia; color usually yellow or brown. The surface has 



