GENUS ACANTHOCYSTIS— ACANTHOCYSTIS ? 269 



I have repeatedly observed a bright-green Heliozoan, which I at first 

 regarded as Acanthocystis chcetophora, but closer examination led to the 

 detection of differences, which render it probable it may belong to another 

 species. It is commonly smaller than the former, and appears of an 

 intensely green color, due to the greater proportion of chlorophyl corpus- 

 cles it contains than is usually the case in A. chcetophora, and as represented 

 in figs. 7, 8, pi. XLIII. The surface of the body is mammillated, and this 

 appears to be independent of the presence of the minute disks of the 

 spinous rays. The latter are more numerous and more delicate than in A. 

 chcetophora, and they are not furcate at the free extremity. The exterior 

 of the body is enveloped in a very finely granular stratum, as seen in fig. 

 7 ; but in other instances this is absent, as represented in fig. 8. 



In association with the bi'ight-green Heliozoans, as just described, or 

 in similar positions others occur resembling them, but differing in being 

 colorless, as represented in figs. 10, 11. In these the usual green corpus- 

 cles are replaced by colorless ones, or the latter may also be absent, when 

 the body consists of a nearly homogeneous granular basis, containing a 

 central nucleus and a few vacuoles. The size of the colorless specimens 

 ranges from 0.028 mm. to 0.048 mm. 



In size and structure, the Heliozoans above described nearly agree 

 with the Acanthocystis spinifcra of Professor Greeff.* In the latter, the body 

 contains variable proportions of bright-yellow corpuscles ; but as these are 

 absent in some individuals, the color of the interior corpuscles would appear 

 not to be an important distinctive character. 



In one instance, in April, in water from a spring in which grew water- 

 cress, I observed a bright-red Heliozoan, as represented in fig. 9. In 

 genei'al constitution it resembled the former, but contained numerous 

 bright-red corpuscles, some colorless ones, and a few green ones. It also 

 contained nearly at opposite poles two large granular spheres, one yellow- 

 ish, the other pale green, which I supposed to be food-balls. 



Late in autumn, on several occasions, I have observed Heliozoans, with 

 sufficient resemblance to the former to lead me to suppose they were of the 

 same kind in an encysted condition. An individual of this character, col- 

 lected with Ceratophyllum, in the canal at Bristol, Pennsylvania, is repre- 

 sented in fig. 12. 



"Arckiv f. mikros. Anatomic, 1809, 493, Taf. xxvii, Fig. 20-23. 



