PLATE XXXI. 



CENTROPYXIS ACULEATA. 



Fig. 1. Inferior view of a living specimen, with psendopods protruded ; shell composed of chiti- 

 noid membrane,, with scattered sand grains, and coarser ones loaded along the fundus. 200 diameters. 

 Spencer pond, Maine, September, 1877. 



Fig. 2. Inferior view of a living individual, with shell of chitinoid membrane and incorporated 

 grains of sand. 200 diameters. Among Chara, in pond on Bushkill Creek, Easton, Pa., June, 1876. 



Fig. 3. Inferior view of a shell composed of brown chitinoid membrane, with incorporated rods 

 and irregular angular plates. 200 diameters. Ditch below Philadelphia. 



Figs. 4, 5. Inferior and inferior oblique views of the same specimen. Shell of chitinoid membrane 

 with scattered sand grains. 200 diameters. Found with the preceding. 



FlGS. 6, 7. Inferior and lateral views of a specimen. Shell of brown chitinoid membrane, finely 

 punctate, and with scattered sand and diatoms. On Utricularia, from Jacksonville, Fla. 



Fig. 8. Inferior view of a shell of brown chitinoid membrane, with incorporated sand along the 

 posterior border. 250 diameters. Sphagnum of Absecom, N. J. 



F?GS. 9, 10. Inferior and lateral views of a shell of chitinoid membrane, with a few incorporated 

 diatoms and sand grains. 250 diameters. Absecom pond, New Jersey. 



Fig. 11. Lateral outline of the shell of a living specimen, composed of chitinoid membrane with 

 sand grains, and with a single spine to the fundus. 250 diameters. Pond on Darby Creek, Pennsylvania. 



Figs. 12, 13. Inferior and lateral views. Shell composed of chitinoid membrane, with scattered 

 grains of sand. 200 +. Sphagnum of Absecom, N. J. 



Fig. 14. Inferior view of an empty shell of brown chitinoid membrane, entirely devoid of foreign 

 matter, and finely and regularly punctate ; but the punctae not resolvable into cancelli as in the shell 

 of Arcella. Ditch below Philadelphia, with Lemna and Wolffia. 



Figs. 15, 10. Inferior and lateral views. 250 -f-. Absecom, N.J. 



Fig. 17. Inferior view of a shell, composed of sand. 200 -{-. Ditches below Philadelphia. 



Figs. 18, 19. Inferior views of two similar specimens. Pond on the Delaware Eiver abovo 

 Easton, Pa. 



Figs. 20, 21. Inferior and lateral views of a specimen, composed of sand united by brown cement. 

 Fort Bridger, Wyoming Territory. 



Fig. 22. Inferior view of a specimen composed of sand. Same locality. 



Figs. 23,24. Inferior and lateral views of a specimen composed of sand. Partridge Island, Nova 

 Scotia. 



Figs. 25, 26. Inferior and lateral views of a small specimen. 500 -|— Dripping rocks of Fairmount 

 Reservoir, Philadelphia. 



Figs. 27, 28. Inferior and lateral views of a shell, composed of chitinoid membrane with sand and 

 dirt. 200 +. Atco, N. J. 



Figs. 29, 30. Inferior and lateral views. 350 -f-. Pond on Darby Creek, Pennsylvania. 



Fig. 31. Inferior view of a shell, except the spines composed of diatoms. 350+. Pokono Mount- 

 ain, Pennsylvania. 



Fig. 32. Inferior view of a shell, composed of diatoms and sand. 500 +. Lake Hattacawanna, 

 New Jersey. 



Figs. 33, 34. Inferior and lateral views of a shell of similar composition, pertaining to the variety 

 Centropyxis ecornis. 500 4-. Abundant form with the preceding. 



Fig. 35. Lateral view of a shell, with spines fore and aft. 200 -f. Ditch below Philadelphia. 



