PLATE XIII. 



DIFFLUGIA ACUMINATA. 



The shell composed of angular particles of quartz sand, except in instances especially mentioned ; 

 the sarcode iu nearly all colorless, or with a pale clay color to the endosarc. 



Figs. 1,2. Examples of common forms in Swarthruore brick-pond, May, 1874. Sarcode colorless 

 and commonly entirely obscured from view by the structure of the shell. 200 diameters. 



Figs. 3, 4. Shells of coarse angular quartz sand. China Lake, Uinta Mountains, Wyoming Terri- 

 tory, August, 1877. Common forms. 250 diameters. 



Fig. 5. Two individuals in conjugation. The coarse structure of the shell prevented any move- 

 ment of the sarcode from being visible ; the yellowish stain produced by the endosarc. Swarthmore 

 brick-pond, May, 1874. 200 diameters. 



Fig. 6. Individual with pseudopods protruded. Pond on Mount Gilbert, Uinta Mountains, Wyo- 

 ming, August, 1877. 250 diameters. 



Fig. 7. Shell of coarse quartz sand. Absecom pond, New Jersey, August, 1876. 200 diameters. 



Fig. 8. Individual with shell approximating the form of that of Difflugia urceolata. China Lake, 

 Uintas. 250 diameters. 



Fig. 9. Tubular form with acuminate summit, not uncommon. Fond on Darby Creek, Delaware 

 County, Pennsylvania, October, 1874. 200 diameters. 



Fig. 10. Small individual found with others of the same kind among Utricularia frorn Florida, 

 October, 1874. 200 diameters. 



Fig. 11. Shell of coarse sand, with a single pointed flake at the acuminate summit. Absecom 

 pond, New Jersey, October, 1874. 500 diameters. 



Fig. 12. Shell of unusual form, with well-defined neck and mouth surrounded with a distinct 

 rim; also composed of comparatively coarse sand. Found in the same gathering as the last. 500 

 diameters. 



Figs. 13-15. From Swarthmorebriek-pond. 200 diameters. Fig. 13, an ordinary form of shell; 

 sarcode with yellowish endosarc ; fig. 14. individual with pseudopods protruded ; fig. 15, individual with 

 pseudopods protruded and with bright green endosarc. The brown spots on the shells of the two latter 

 figures indicate grains of garnet ■ ntcriug into their construction, an unusual occurrence. 



Fig. 16. Unsymmetrical shell, with unusually large stone adherent on one side. China Lake, 

 Uintas, Wyoming T. 250 diameters. 



Figs. 17, 18. Shells of chitinoid membrane with incorporated sand. Pond at Atco, N. J., August, 

 1876. 250 diameters. 



Fig. 19. Shell of chitinoid membrane, with incorporated sand and diatom fragments. Absecom 

 pond, New Jersey, August, 1876. 250 diameters. 



Figs. 20-22. Drop tube-like forms. Absecom pond, New Jersey. 200 diameters. Fig. 20. Indi- 

 vidual with unusually and remarkably rough shell, composed of sand; September, 1875. Fig. 21. Shell 

 remarkably uneven, composed of chitinoid membrane with incorporated sand and diatoms ; October, 

 1871. Fig. 22. Shell of chitinoid membrane with incorporated sand and diatoms; found in company 

 with the last. 



Figs. 23-26. Shells of chitinoid membrane incorporated with diatoms; 23-25 empty, and the for- 

 mer with sand at the border of the mouth : 26, with the sarcode encysted. From sphagnum of Abse- 

 com cedar swamp, October, 1874. 500 diameters. 



