GENUS DIFFLUGIA— DIFFLUGIA AltCULA. 117 



of yellowish chitinoid membrane, mostly with more or less adherent dirt or 

 scattered particles of quartz-sand or diatoms, especially occupying the 

 fundus. 



Size. — From 0.112 mm. to 0.144 mm. broad by 0.06 mm. to 0.08 mm. 

 high; mouth 0.028 mm. to 0.04 mm wide. 



Locality. — Sphagnum of Atco and Absecom, New Jersey; of Toby- 

 hanna, Pokono Mountain, Monroe County, and Broad Mountain, Schuylkill 

 County, Pennsylvania. 



Difflugia arcula is perhaps an extreme variety of Difflugia lobostoma. 

 It is not unfrequent, and appears to be confined to sphagnous swamps. In 

 shape, color, and material of structure, its shell resembles that of an 

 Arcella, as seen in figs. 34-37, pi. XV. Usually it is nearly hemisphe- 

 roidal; but the height is commonly a little greater than half the breadth. 

 The top is evenly rounded and dome-like. The bottom is a broad, shallow, 

 inverted funnel with reflected border. The mouth is central and trilobed; 

 the lobes or sinuses being variably narrowed in degree. See figs. 34-37, 

 pi. XV; figs. 30, 31, pi. XVI. 



In structure, the shell is composed of chitinoid membrane of different 

 shades of straw-color, often with irregular darker spots, apparently as if 

 due to adherent dirt. Frequently, also, it has incorporated particles of 

 hyaline quartz-sand mostly scattered on the sides, or more especially 

 accumulated on the fundus. Sometimes a few diatoms or fragments of 

 these are mingled with the quartz-sand. 



The specimens observed were always dead, so that I did not ascertain 

 the appearance of the sarcode. 



The smallest specimen measured id of an inch broad and id of an 

 inch high; the largest was id of an inch broad and i^th of an inch high. 



Difflugia arcula probably merges into D. gldbulosa, D. lobostoma, Centro- 



pyxis, and Arcella. 



DIFFLUGIA CORONA. 



Plate XVII. 



Difflugia corona. Wallich: An. Mag. Nat. Hist, xiii, 1864.— Leidy : Pr. Ac. Nat, So. 1874, 14, 79; 1877 307. 

 Difflugia protciformis, subsp. D. globuJaris, var. D. corona. Wallich: Ibid. 



Shell spherical or spheroidal, composed of clear angular quartz-sand; 

 fundus with a number of conical spines of the same composition as the rest 

 of the shell; mouth terminal, circular, with the border multidentate or 



