PLATE XII. 



Figs. 1-18.— DIFFLUGIA PYRIFORMIS. 



Fig. 1. Individual with shell of uniform transverse diameters, but with less prolonged neck than 

 usual. The contracted sarcode with bright green endosarc. Absecom pond, September, 1875. 100 

 diameters. 



Figs. 2-9. The variety Diffiugia vas distinguished by a constriction in the neck of the shell. 



Fig. 2. Individual from the same gathering as that of fig. 1. 100+ . 



Fig. 3. Empty shell of coarse sand grains. Ft. Bridger, Wyoming. 



Figs. 4-6. Individuals with shell st.iined ' ly ferruginous coloring. Sphagnous bog near Abse- 

 com, October, 1875. 100 diameters. 



Fig. 7. Small, empty shell, somewhat unsymmotrical and of comparatively even surface. Swarth- 

 moro brick-pond, Ai>ril, 1876. 350 diameters. 



Fig. 8. Individual with comparatively even shell, and with endosarc mingled green and yellow. 

 Found with the last. 350 +. 



Fig. 9. Large individual with shell of coarse sand, and with sarcodo contracted into a ball ; the 

 endosarc exteriorly green and centrally yellow. Budd's L.ake, New Jersey, March, 1875. 100 diameters. 



Figs. 10-16. The variety Diffiugia compressa, in which the shell is broader one way than in the 

 other. 



Figs. 10, 11. Two views of the same individual in outline. The yellow spot indicates the appear- 

 ance of the endosarc. Spring on Darby Creek, Delaware County, Pennsylvania. 100 diameters. 



Figs. 12, 13. Two views of an individual. The aarcode retracted but not encysted; the endosarc 

 yellow. From material collected on South Mountain, Burke County, North Carolina. 200 diameters. 



Fig. 14. Individual with shell composed of coarse sand, uneven surface and slightly-pointed sum- 

 mit. 200 diameters. Breadth 0.22 mm. by 0.112 mm. 



Figs. 15, 16. Two views of an individual, with shell of coarse sand .and yellow endosarc. 200 

 diameters. This and the preceding from a pond on Darby Creek, Delaware County, Pennsylvania. 



Figs. 17, 18. The variety Diffiugia cm-nuta. Both in outline ; 250 diameters. From a bog near 

 Atco, N. J., June, 1877. One with one, the other with two points, and both with colorless sarcode. 



Figs. 19-21.— DIFFLUGIA CRATERA. 



Figs. 19,20. Two empty shells composed of chitinoid membrane with incorporated granules of 

 sand. From Bristol Canal, Bucks County, August, 1876. 600 diameters. 



Fig. 21. Empty shell. Lake Erie, Buffalo, N. Y., August, 1878. 800 diameters. 



(Since describing these minute forms I have suspected that they belong to a ciliated infusoriau of 

 the genus Tintinnus.) 



Figs. 22, 23.— DIFFLUGIA URCEOLATA. 



Common forms in China Lake, Uinta Mountains, Wyoming Territory, August, 1877. 125 

 diameters. 



Figs. 24-28.— DIFFLUGIA ACUMINATA. 



Compressed variety with from one to three spines to the fundus of the shell. 



Figs. 24-27. Specimens from Swarthmore brick-pond, June, 1874. 350 diameters. Fig. 24. With 

 a single spine ; breadth 0.088 mm. by 0.052 mm. Fig. 25. With a pair of spines ; breadth 0.072 mm. by 

 0.052 mm. Fig. 26. With two spines of unequallength; breadth 0.064 mm. by 0.048 mm. Fig. 27. 

 With three spines; breadth 0.072 mm. by 0.056 mm. 



Figs. 28, 29. Two views of the same individual. Fig. 28. Broader view, with pseudopods pro- 

 truded, and animal as observed in the act of swallowing a diatom. Fig. 29. Narrower view. From a 

 ditch below Philadelphia, August, 1874. 200 diameters. 



In this plate the lithographer has greatly exaggerated the yellow coloring. In figs. 4-6 the shells 

 had a faint fen-uginous tint ; in figs. 8, 9, the color pertaining to the sarcode was browner and duller ; 

 in figs. 15, 16, and 22-28 the color was pale clay colored, and in figs. 19-21 the shell was nearly colorless. 



