HOLOTRICHA 561 



fractile granules; macronucleus posterior; contractile vacuole be- 

 tween nuclei and peristome, with a slit-like aperture (Fig. 27); 

 65-1 25Ai by 47-86^; in mantle cavity, gills and on non-ciliated 

 surface of palps of Elliptio cornplanatiis; Woods Hole. 



C. curtus Engelmann. Somewhat broader; 60-125^ by 50-90^1; 

 peristomal field smaller; cytopharynx less conspicuous, but long- 

 er; ciliation dense; endoplasmic granules are more closely packed 

 and do not extend as far out toward anterior end; macronucleus 

 central; Kidder found this ciliate in the mantle cavity of Anodon- 

 ta marginata, A. implicata, A. catareda, Lampsilis radiata, L. 

 cariosa and Alasmidonta undulata which were obtained from the 

 freshwater lakes of Massachusetts and New York. 



C. magna Kidder. Much larger; 123-203ju by 63-116//; closer 

 cihation; anterior 1/3 filled with smaller granules; irregularly 

 outlined macronucleus, 25-30)U in diameter, central; 2 (or 1) 

 micronuclei ; aperture for contractile vacuole large ; mantle cavity 

 of Elliptio complanatus ; Massachusetts. 



C. caryoclada K. (Fig. 255, h). Oval; extremely flattened; leaf- 

 like ; cytostome small, in posterior fourth ; macronucleus conspic- 

 uously branched; 2 (1) micronuclei; 140-250^ by 90-160/^; mantle 

 cavity of the edible clam, Siliqua patula; Oregon. 



C. mytili De Morgan (Fig. 53). Reniform; 130-202^ by 76- 

 16 1m; peristomal groove on right side; trichocysts conspicuous 

 along frontal margin; macronucleus oval; 2 micronuclei. Kidder 

 (1933) found the organism on the foot of the common mussel, 

 Mytilus edulis, in New York and studied its division and conju- 

 gation. 



Genus Myxophyllum Raabe. Oval or spheroid; pellicle elastic 

 and flexible; peristome on posterior right, without undulating 

 membrane; 7 macronuclei; a micronucleus; ciliation uniform; in 

 the slime covering land pulmonates. 



M. steenstrupi (Stein) (Fig. 255, c). 120m by 100-120^; on Suc- 

 cinea putris, etc. 



Family 2 Thigmophryidae Chatton et Lwoff 



Genus Thigmophrya Chatton et Lwoff. Elongate; round or ob- 

 long in cross-section; cytostome in posterior third; contractile 

 vacuole opens in cytopharynx; on gills or palps of lamellibranchs. 



T. macomae C. et L. Elongate ovoid; flattened; ventral surface 

 slightly concave; oral funnel opened; contractile vacuole opens at 



