ARCHER JNA BOLTONI. 115 



plasmodium, that is to say, is not formed by fusion of 

 independent amoeba forms, but is due to continuous 

 growth. When nutrition fails, the individual chloro- 

 phyl corpuscles separate, each carrying with it an 

 investment of protoplasm, and then each such amoeba 

 form forms a cyst around itself, which is covered with 

 short spines. The cysts are not known to give rise to 

 spines, but appear to be merely hypnocysts. The 

 domination of the protoplasm by the chlorophyl cor- 

 puscles is very remarkable and unlike anything known 

 in any other organism. Possibly the chlorophyl cor- 

 puscles are to be regarded as nuclei, since it is known 

 that there are distinct points of affinity between the 

 dense protoplasm of ordinary nuclei and the similarly 

 dense protoplasm of normal chlorophyl corpuscles." 



Order II. CONCHULINA. 



Family 1. ARCELLIDA. 



Test simple, transparent, homogeneous, or composed 

 of numerous and variously-formed chitinoid plates, or 

 opaque from encrustation with sand-grains or other 

 extraneous material ; monothalmous ; pseudopodia 

 mostly digitate, rarely lobular ; nucleus single or mul- 

 tiple; contractile vesicles one or several. 



SYNOPSIS or THE GENERA. 



Test discoid, membranous ; in dorsal view circular, 

 laterally hemispherical or depressed ; mouth central. 



15. Arcella. 



Test discoid, circular, flexible in the young state, the 

 outer lamina extremely thin ; oral aperture irregular 

 and rarely distinguishable. 16. Pseudochlamys. 



Test discoid, with a circular or broadly oval, some- 

 times irregular outline, obtusely rounded and thickened 

 posteriorly ; the oral aperture excentric, round, oval, 

 or lobate. 17. Centropyseis. 



