2 26 FRESH-WATER BIOLOGY 



79 (80) Inferior lip rounded, dipping far into the interior of the shell. 



Plagiopyxis calUda Penard 1910. 



Shell gray, yellow, or brown in color, usually smooth and clear. The 

 lips overlap to such an extent that the aperture is ditlicult to observe. 

 v\r--l Pseudopodia large at the base with furcate extremities. Nucleus single. 

 Kj-^K!'] Diameter g2 to 103 /i- Habitat mosses. 



Fig. 310. Plagiopyxis callida. X 150. (.^fter Wailes and Penard.) 



80 (79) Inferior lip triangular, slightly dipping into the interior of the shell. 



Plagiopyxis lahiata Penard 191 1. 



Brown in color. Smaller than the preceding species. Nucleus sin- 

 gle. Pseudopodia not observed by Dr. Penard, who reports the species 

 from Australia and Vancouver, B. C. Diameter 80 to 88 p. 



Fig. 311. Plagiopyxis labiata. X 155. (After Penard.) 



81 (76) Shell more or less compressed; aperture not lunate 82 



82 (83) Plates quadrangular Qiuidndella Cockerell. 



Representative species. . Quadmlella symmetrica F. E. Schultze 1875. 



In this species the shell is normally pyriform, one variety 



^ being short and another long. The plates are very transparent, 



usually regularly arranged in transverse and longitudinal series. 



;rt>/J;;'?^^ Pseudopodia few. Common in sphagnous swamps. Length 



from 80 to 140 ^l. 



Fig. 312. Quadrulella symmetrica, cv, contractile vacuole. X i7S- 

 (After Leidy.) 



83 (82) Plates not quadrangular 84 



84 (91) Shell pyriform, sometimes ovoid or rounded, compressed with round, 



oval, or irregular plates Nebela Leidy . . 85 



85 (88) Shell pyriform 86 



86 (87) Neck long, narrow; plates round. . Nebela lageniformis Penard 1890. 



Body of shell oval, prolonged as a tubular neck. There are no 

 'j—onc^ ^^^\ lateral pores through the shell as in some species. The plates are 



fo^^^^^^^of'^^^fl round and very clear. Pseudopodia few. Found commonly 



\<r£ii22£Q2hxi^^^-Ci.(^^ among mosses; very abundant in some localities. Length 125 n. 



^Ss=^ Fig. 313. Nebela lageniformis. X i7S- (After Penard.) 



87(86) Neck short; plates round or oval. . . . Nebela collaris Leidy iSyg. 



In this species, large, round, and oval plates are usually inter- 



A r!^^??3?^?^ySl^^^^ mingled. Sometimes foreign elements enter into the composition 



^c^--.>o^ _..{^^4^ of the shell. It is a ver>' common species, found abundantly in 



'••o.;,.;^-^M,a.J<9 sphagnous swamps and presents many variations in size and form. 



Large individuals average about 1 20 /x. 



Fig. 314. Nebela collaris. X 150. (After Leidy.) 



88 (85) Shell not pyriform 89 



89 (90) Shell rounded, border of aperture smooth. 



Nebela flabell urn Leidy 1874. 

 The transverse diameter usually equals or exceeds the length, but 

 'pypJ'?^h. apparently transitional forms between this species and the preceding 



jm^ooo'^W^ one are sometimes observed. Possibly this is but a variety of Nebela 

 W^^^OQ^^ collans. The plates are similar in the two species. Habitat sphagnous 

 '^°-^'?^Sct^ swamps. Length 50 to 100 m- 



Fig. 3x5. Nebela Jiabellum. X 150. (After Leidy.) 



