346 



FRESH-WATER BIOLOGY 



52 (48) The dorsal transverse piece between the longitudinal stalks has a 

 single median chitinous spine 53 



53 (54) The median point is rudimentary; much shorter than the terminal 

 branches Dalyellia viridis (G. Shaw) 1791. 



Length 5 mm. Unpigmented except during the maturing of the eggs 

 when there is a brownish pigment, but with a continuous layer of zoo- 

 chlorellae under the integument giving the characteristic green color. 

 Rochester, N. Y. 



Fig. 613. Dalyellia viridis. Chitinous portion of cirrus: si, two-parted stalk; 

 ea, terminal branch. Much enlarged. (After von Graff.) 



54 (53) The median point is as long as the terminal branches 55 



55 (56) One terminal branch is not jointed but consists of a single piece 

 shaped Uke a plow-share, and does not have spines. 



Dalyellia armigera (O. Schmidt) 1861. 



I 



Length 0.6 to 1.5 mm. Color yellowish, reddish, or 

 brownish-gray. Pharj^nx very large, almost one-fourth 

 of entire length of body. Anterior end blunt, tail with 

 adhesive papillae. Swims actively at the surface of stand- 

 ing and running water. Brooks, Monroe Co., N, Y.; 

 Lake St. Clair, Mich. 



Fig. 614. Dalyellia armigera. ^ (A ) living, uncompressed. X 5°- 

 (B) chitinous portion of cirrus' m, median point; ea, terminal 

 branch with 3 to g (mostly 7 or 8) spines; ea2. terminal branch 

 shaped like a plow-share; g, dorsal and ventral cross pieces; 

 St, stalk. X 500. (After von Graff.) 



56 (55) Both terminal branches bear a row of plates or spines. 



57' 



