226 



FRESH-WATER BIOLOGY 



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



Plagiopyxis callida Penard 1910. 



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

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

 Pseudopodia large at the base with furcate extremities. Nucleus single. 

 Diameter 92 to 103 it. Habitat mosses. 



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



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



Plagiopyxis labiata 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 Austraha and Vancouver, B. C. Diameter 80 to 88 ft. 



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



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



82 (83) Plates quadrangular. .... . Quadrulella CockereU. 



Representative species. 



Quadrulella 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. 

 Pseudopodia few. Common in sphagnous swamps. Length 

 from 80 to 140 li. 



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 

 lateral pores through the shell as in some species. The plates are 

 round and very clear. Pseudopodia few. Found commonly 

 among mosses; very abundant in some localities. Length 125 11. 



Fig. 313. NeMa lageniformis. X 175. (After Penard.) 



87 (86) Neck short; plates round or oval. . Nebela collaris Leidy 1879. 



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

 mingled. Sometimes foreign elements enter into the composition 

 of the shell. It is a very common species, found abundantly in 

 sphagnous swamps and presents many variations in size and form. 

 Large individuals average about 1 20 (i. 



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



88 (8s) Shell not pyriform 89 



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



Nebela flabellum Leidy 1874. 

 The transverse diameter usually equals or exceeds the length, but 

 apparently transitional forms between this species and the preceding 

 one are sometimes observed. Possibly this is but a variety of Nebela 

 collaris. The plates are similar in the two species. Habitat sphagnous 

 swamps. Length 50 to 100 11. 



Fig. 315. Nebela flabellum. X 150. (After Leidy.) 



