PLATE XXVIII. 



Figs. 1-7— ARCELLA VULGARIS. 



Fig. 1. Lateral view of a pair in conjugation, in one of -which tho shell is colorless. Tho mssaos 

 of Barcode as observed were not in union. Egg Harhor, N. J., September, 1877. 500 diameters. 



Fig. 2. Lateral view of an empty shell, with an even dome. Absecom, N. J. COO diameters. 



Fig. 3. Lateral view of a specimen, with the sareode forming a large encysted ball, and causing 

 the eversion of the usual funnel-like base of the shell. Same, locality, March, 187C. 350 -f. 



Figs. 4,5. Inferior* and lateral views of an empty shell, with depressed fundus. Found with tho 

 preceding. 350 -f . 



Figs, (i, 7. Superior and lateral views of a shell of quadrate outline, and depressed fundus. Pond 

 on Pokono Mountain, Pennsylvania, July, 1870. 250 -f. 



Figs. 8-13.— ARCELLA VULGARIS, var. angulosa. 



Figs. 8, 9. Superior and lateral views of the same specimen, the former represented without the 

 sareode. Woodstown pond, New Jersey, September, 1877. 250 +. 



Figs. 10, 11. Superior and lateral views of a similar specimen, found with the preceding. The 

 sareode not represented. 



Figs. 12, 13. Superior and lateral views of another, and similar specimen found with the pre- 

 ceding. 



Figs. 14-38.— ARCELLA DISCOIDES. 



Figs. 14, 15. Inferior and lateral views of an individual. Iu tho sareode of the former a pail of 

 opposite nuclei and several contractile vesicles visible. Swarthmore brick-pond, Delaware County, 

 Pa., September, 1874. 350 -f. 



Figs. 16, 17. Inferior and lateral views of another individual found with the former. 



Fig. 18. Lateral view of a shell. China Lake, Uinta Mountains, Wyoming Territory. 250 -f. 



Figs. 19-21. Lateral views of three shells from living specimens. Woodstown pond, New Jersey, 

 September, 1877. Fig. 19 is inadvertently unsymmetrical, and should he the same on the right as on 

 the left. 



Fig. 22. Lateral view of a large individual, with extended pseudopods. As exemplified in this 

 figure, while the mass of sareode within tho shell and the pseudopods exterior to the base are visible, 

 the intermediate port ions extending through the funnel, from their transparency, cannot be seen. Fort 

 Bridger, Wyoming Territory, August, 1877. 250 -)-. 



FlG. 23. Inferior view of a nearly colorless individual. Tho sareode exhibits a pair of opposite 

 nuclei and seven conspicuous contractile vesicles. Absecom pond, N. J., April, 1875. 350-)-. Theheight 

 of the shell was about one-third tho breadth. 



Fig. 24. Inferior view of an individual, with projected pseudopods. The sareode exhibts a pair 

 of nuclei, four contractile vesicles, and on the right upper border a large air-bubble. Fig. 25. Lateral 

 view of tho shell of tho same. Bristol Canal, Pennsylvania, September, 1876. 500 -(-. 



Figs. 28, 27. Inferior and lateral views from the same individual. In the interior sareode of the 

 former the two opposite nuclei are seen, and at tho border five contractile vesicles. Pond on Darby 

 Creek, Delaware County, Pennsylvania, April, 1876. 500 -f . 



FlG. 28. Inferior view of a large individual (correct outline, though not quite regularly circular). 

 Three nuclei visible iu the sareode ; and a number of contractile vesicles at the border. On Utricularia, 

 from Jacksonville, Florida, May, 1875. 266 -f. 



Fig. 29. Inferior view of a colorless individual, acted on by an ammoniacal solution of carmine ; 

 tho nuclei as they appeared stained deep red. Absecom pond, New Jersey, June, 1874. 350 -(-. 



Figs. 30, 31. Two views of the same individual. Tho shell pale yellowish, very thin and flexible. 

 China Lake, Uinta Mountains, Wyoming Territory, August, 1877. 500 -f-. 



Fig. 32. Inferior view of an empty shell with quadratcly rounded outline and oval mouth. 

 Jacksonville, Fla. 250 +. 



Fig. 33. Lateral view of a specimen, having the same shape as the former in the inferior view. 

 Found with the preceding. 



Fig. 34. Inferior view of a specimen with oval outline. With the preceding. 



FlGS. 35, 36. Inferior and lateral views of a specimen; the former with oval outline, and oval 

 mouth whoso long diameter crosses that of the shell. (The lithographer has inadvertently colored the 

 two figures differently.) Found with the preceding. 



Fig. 37. Inferior view of a shell with oval outline and mouth. Absecom pond, New Jersey. 



Fig. 38. Inferior view of shell, with trilobate outline and oval mouth. With the preceding. 



* In the empty shells, when transparent, tho inferior and superior views appear the same. 



