184 FRESH- WATEE EHIZOPODS OF NORTH AMERICA. 



to see the sarcode so as to distinguish its different elements. Mostly, the 

 structure of the shell was such as to obscure the interior soft structure, 

 and generally it has so happened that in specimens in which the shell was 

 transparent, it was almost invariably empty. 



Centropyxis is frequently found among floating conferva?, or among 

 the flocculent materials, with desmids, diatoms, and other alga?, adherent to 

 aquatic plants. . The spines of the shell would appear to enable it to main- 

 tain its position. According to Claparede and Lachmann, delicate pseudo- 

 pods are transmitted by the spines ; but this fact I have not observed. The 

 ordinary pseudopods are protruded usually a few at a time, and they 

 present the same appearance as in Difflugia and Arcella. 



Smaller specimens of the variety Centropyxis ecornis, so far as the 

 shell is concerned, become undistinguishable from the smaller, spineless 

 kinds of Difflugia constricta. 



Forms recently described by Professor Barnard, under the names of 

 Ecliinopyxis tentorium and E. hemispherica (Am. Quart. Micros. Jour. 1879, 

 84, pi. viii, figs. 1, 2), found in association with Centropyxis aculeata, in 

 creeks and ponds of New York, I have not observed. The figures of the 

 former, E. tentorium, remind me of the single-spined variety of Difflugia con- 

 stricta, as represented in fig. 51, pi. XVIII. 



COCHLIOPODIUM. 



Greek, cocldis, a shell ; pons, a foot. 

 Amwba: Auerbach. Amphizonella : Archer. CocMiopodium ; Hert wig ami Lesser. 



Animal minute, provided with a flexible, chitinoid shell thinning away 

 to the broadly expansive mouth, and exhibiting a minutely cancellated 

 structure. Sarcode intimately adherent to every part of the interior of the 

 shell, pale granular, mingled with variable proportions of highly refractive 

 corpuscles, often crystals and other elements, together with a large central 

 nucleus and one or more contractile vesicles. Pseudopods delicate, hya- 

 line, conical, pointed, and sometimes forking. 



COCHLIOPODIUM BILIMBOSUM. 



Plate XXXII, figs. 1-25. 



Amoeba bilimbosa. Auerbach : Zeits. -wis. Zool. vii, 1856, 374, Taf. xix, Fig. 1-13. 

 Amoeba actinophora. Auerbach: Ibidem, 392, Taf. xx. 

 AmwDa zonalis. Leidy: Proc. Acad. Nat. Sc. 1874, 87. 



CocMiopodium pellucidum. Hertwig and Lesser: Arch. mikr. Anat. x, 1874, Suppl. 06, Taf. ii, Fig. 7.— 

 Schulze : Ibidem, xi, 1875, 337, Taf. xix, Fig. 1-5. 



