PLATE XLIII. 



Figs. 1-6.— ACANTHOCYSTIS CHiETOPHOEA. 



Fig. 1. A green indivitlual. Cominon form, in the vicinity of Philadelphia, among vaiioos 

 aquatic plants. Ditches below Philadelphia, September, 1874. 750 diameters. 



Fig. 2. One of the longer furcate spines more highly magnified. 



Fig. 3. One of the smaller furcate spines more highly magnified. 



Fig. 4. A colorless individual. Less common than the former variety. Swarthmore brick-pond, 

 Delaware County, Pennsylvania, May, 1874. 1,000 diameters. 



Fig. 5. An elliptical form, supposed to pertain to the same. Absecom pond. New Jersey, Septem- 

 ber, 1874. 27.5 diameters. • 



Fig. 6. Supposed shed capsule, containing a few green grains and a brownish ovum-Uke body. 

 Fort Bridger, Wyoming Territory, July, 1877. 250 diameters. The capsule was crowded with long and 

 short furcate spines like those of the figure. 



Figs. 7-12.— ACANTHOCYSTIS ? With simple spines. 



Fig. 7. Bright green individual. Fort Bridger, Wyoming Territory, August, 1877. 750 diameters. 



Fig. 8. Green individual. Fort Bridger, July, 1877. 500 diameters. 



Fig. 9. A bright red individual. Spring on Darby Creek, Delaware County, April, 1875. 700 

 diameters. 



Fig. 10. A colorless individu.il. Atco, N. J., October, 1877. 666 diameters. 



Fig. 11. Colorless individual. Broad Mountain, Pennsylvania, September, 1876. 500 diameters. 



Fig. 12. Colorless individual, with the protoplasmic mass in an encysted condition, enclosed in a 

 spinous capsule. With Ceratophyllum, from Bristol Canal, Pennsylvania, December, 1877. 666 

 diameters. 



Fig. 13. Fragment of membrane, supposed to be a portion of a moulted capsule of Acanthooystis. 

 Fort Bridger, Wyoming, August, 1877. 500 diameters. 



Figs. 14-16.— ACANTHOCYSTIS ? With short pin;Uke spinas. 



Fig. 14. Individual, with the interior occupied by a mass of protoplasm com aiuiug a nucleus and 

 a vacuole, but emitting no pseudopodal rays. 



Fig. 15. An individual with the protoplasm contracted into a baU, floating In a thinner liquor, 

 and exhibiting at the periphery three vacuoles. 



Fig. 16. An individual with the interior protoplasmic mass apparently ready to assume tha 

 encysted state.^ All three specimens collected with others in a pond in Fairmount Park, West Philadel- 

 phia, August, 1878. 663 diameters.- 



