TLATE XXVII. 



ARCELLA VULGARIS. 



In most of the figures of Arcella in this arid the succeeding plates the cancellated or dotted appear- 

 ance of the shell is omitted. The color is less varied than in the originals. 



Figs. 1,2. Lateral and inferior views of the same individual, with extended pseudopods. Bog on 

 the Schuylkill, West Philadelphia, June, 1877. 250 -f. 



Fig. 3. Lateral view of an empty shell. Ditch below Philadelphia. 250 +. 



Fig. 4. Lateral view of a colorless, transparent individual, with projected pseudopods, and sar- 

 code attached to the interior of the shell by tapering threads. Swarthmore brick-pond, Delaware 

 County, Pa., September, 1874. 500 +. 



Fig. 5. Individual with colored shell, the sarcode visible within. Same locality, and magnified 

 same degree. 



Fig. 6. Shell of a small individual. Original was living, and the shell of a brown color. Fort 

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



Fig. 7. Lateral view of an active individual, with sarcode risible, with protruded pseudopods, 

 and with pale yellow shell. Absecom pond, N. J., April, 1876. 350 +. 



Fig. 8. Upper view of a colorless individual. The sarcode attached by tapering threads to the 

 interior of the shell ; around its border five contractile vesicles visible, and more internally a pair of 

 nuclei opposite each other. The dotted appearance of the shell represents the cancellated structure. 

 a, one of the nuclei. Fairmount Park, Philadelphia, June, 1878. 250 -f-. 



Figs. 9, 10. Two views of the shell from a living specimen ; inferior view showing a crenulated 

 mouth, and lateral view showing the inflection of the base to the mouth. Absecom pond, New Jersey, 

 August, 187(5. 350 -f . 



Figs. 11, 12. Lateral and upper views of an individual, with the sarcode visible, and with pro- 

 jected pseudopods. a, nuclei ; b, contractile vesicle ; c, amceboid corpuscles iu the interval between 

 the sarcode and the shell ; d, large air-bubble. Fairmount Park, June, 1877. 250 -f. 



Fki. 13. Inferior view of a similar specimen. Ditch below Philadelphia, September, 1877. 250 +. 



Figs. 14, 15. Inferior and lateral views of the same individual. In the former view the sarcode 

 appears of irregular form, and it exhibits a single nucleus and three contractile vesicles. Absecom 

 pond, New Jersey, June, 1877. 250 -f . 



Fig. 16. Small shell (of a dark ochreous color) with pitted surface. Woodstown pond, New Jer- 

 sey, September, 1877. 250 +. 



Fig. 17. Side view of a pair of individuals in conjugation, both of the same size; the shell of one 

 darker than the other. Swarthmore brick-pond, September, 1874. 250 -f-. 



Fig. 18. Inferior view of a specimen, living and active, in which portions of the shell appeal- as 

 if bitten out. Atco, N. J., June, 1877. 250 +. 



Figs. 19,20. Inferior and lateral views of an individual, with constricted shell. Fairmount Park, 

 Philadelphia, May, 1878. 250 +. 



Figs. 21,22. Upper views of two minute specimens, probably young individuals, with the sarcode 

 showing a single nucleus and several large contractile vesicles. Atco, N. J., October, 1877. 1,000 -f-. 



Fig. 23. Lateral view of a living specimen, with pitted shell. China Lake, Uinta MtSBitaius, 

 Wyoming Territory, August, 1877. 500 +. 



Fig. 24. Two similar individuals in conjugation, with the shells of different shades of color. With 

 I he preceding. 



Figs. 25, 25. Inferior and lateral views of an individual, with pitted shell. Swarthmore, Delaware 

 County, Pa., April, 1874. 350 +. 



Figs. 27, 28. Superior and lateral views of an empty shell, with irregularly pitted surface. Same 

 locality. 



Figs. 29, 30. Lateral and inferior views of an individual, with pitted shell. Ditch below Phila- 

 delphia, June, 1876. 350 +. 



Fig. 31. Lateral view of a specimen. Fort Bridger, Wyoming Territory, August, 1877. 250 -4-. 



Figs. 32, 33. Lateral and inferior views of a specimen, with the sarcode encysted, and surrounded 

 with llocculent matter, probably excrementitious. Atco, N. J., June, 1*77. 5(0 +. 



FlG.34. Upper view of an empty colorless shell. Swarthmore brick-pond, September, 1874. 350 + 



FlG. 35. Cancellated structure of the shell of Arcella highly magnified. 



