110 FRESH- WATER EHIZOPODS OF NORTH AMERICA. 



into a nipple- shaped process, rarely with two or three points ; neck long, 

 short, or none; mouth large, terminal, circular; lip usually straight. Com- 

 posed of angular quartz-sand, sometimes with intermingled diatoms, rarely 

 of the latter altogether, sometimes of chitinoid membrane with scattered 

 sand and diatoms. Sarcode colorless ; pseudoj:>ods as usual in the genus. 



Size. — Smallest specimens with shell of sand were 0.1 mm. long, 

 0.048 mm. broad, and 0.032 mm. wide at the mouth; large pyriform 

 specimens of sand, 0.4 mm. long, 0.184 mm. broad, and 0.064 wide at the 

 mouth; largest cylindroid ones of stones, 0.520 mm. long, 0.12 mm. broad, 

 and 0.1 mm. wide at the mouth. Smallest specimens with the shell of 

 diatoms measured about 0.084 mm. long, 0.036 mm. broad, and 0.024 mm. 

 at the mouth. 



Locality. — Ditches near Philadelphia, Swartkmore pond, Darby pond, 

 Pennsylvania ; Absecom pond, and ponds of Atco, Kirkwood, and other 

 spbagnous swamps of New Jersey ; ponds at Fort Bridger and Uinta 

 Mountains, Wyoming Territory. France, Leclerc ; Berlin, Ehrenberg ; 

 Switzerland, Perty ; England, Carter and Wallich. 



The shell of DaSSlcayin acuminata in shape is like an ancient Roman 

 amphora, or is oblong oval, gradually narrowing toward the oral extrem- 

 ity, and acute or tapering at the summit ; or it is pyriform, with the fundus 

 in the latter condition ; or it is cylindroid, more or less inflated above, and 

 tapering at the fundus. See pi. XIII. The mouth is terminal, circular, 

 and large, with the lip straight or slightly contracted and rarely slightly 

 everted. In one instance only, as seen in fig. 12, have I seen it surrounded 

 by a projecting rim. The shell either narrows from the body gradually 

 and regularly to the mouth, or more or less abruptly, forming a neck of 

 variable length, sometimes short, sometimes long, and of every interme- 

 diate degree. The longer-necked varieties present us with the pyriform 

 and drop-tube-like shells. 



The fundus of the shell presents various degrees of acuteness, passing 

 into a more or less acuminate condition or prolonged into a nipple-like pro- 

 cess, which may be short and thick, or long and narrow. The process is 

 usually straight, but is often bent to one side, and sometimes occupies 

 a position unsymmetrically to one side. Rarely there are two or three 

 processes to the fundus, as seen in figs. 25-29, pi. XII. 



The amphora-like specimens of Difflugia acuminata graduate into D. 



