EDMONDSON — PROTOZOA OF IOWA. 



19 



Centropyxis may be considered as an intermediate form between 

 Arcella and Difflugia, resembling the latter, however, more than 

 the former. The appearance of Ceniropyxis is as if Difflugia were 

 compressed dorso-ventrally and laterally, resulting in the eccen- 

 tricity of the mouth and fundus. Of the foreign material making 

 up the shell, quartz sand predominates, thus giving to the organ- 

 ism the external appearance of Difflugia, its coloration, however, 

 usually being some shade of brown. 



The fundus is often provided with spines which are longer and 

 more slender than those of Difflugia and which are seldom with 

 any addition of foreign material. 



From one to six or eight spines are usually present. A spine- 

 less variety has been observed on a few occasions in this state. 



Ceyitropyxis is noted for its shyness. Only once have I found 

 the species in an active condition. Fig. 28 illustrates a lateral 

 view of the active individual with a single, long, cylindrical pseu- 

 dopodium extended. Fig. 27 is a ventral view of a spined form. 



Centropyxis aculeata is widely distributed over the state, fre- 

 quently found in great numbers among algae. 



COCHLIOPODIUM Hertwig and Les.ser. 



Shell a delicate, transparent membrane, exceedingly flexible. 

 Protoplasm granular and in close contact with the inner surface 

 of the shell. Mouth capable of becoming greatly expanded as its 

 borders are reflexed. 



COCHLIPODIUM BII^IMBOSUM lyCidy. 



Body with the characters of the genus but having no hair-like 

 appendages. Endoplasm colorless. ■ 



Diameter of shell, 60-90 microns. (Fig. 29, PI. V.) 



This minute organism in general appearance somewhat resem- 

 bles Amoeba, and Auerbach first described it as belonging to that 

 genus. The shell is very plastic and corresponds to the amoeboid 

 movements of which the animal is capable. 



When viewed from above sometimes the body .seems to be sur- 

 rounded by a zone of exuded protoplasm, this appearance, how- 

 ever, being due to the great reflection of that region of the shell 

 bordering the mouth. This great expanse of the mouth may be 

 observed when the organism is viewed laterally, the membranous 

 shell then appearing as a double contour line bordering the body. 



