HOLOTRICHA 563 



T. trisula C and B. (Fig. 268, a). 150-300/x long; length: width 

 3 : 1-2 : 1 ; ponds in Pennsylvania and California ( Wenrich). 



Family 2 Metacystidae Kahl 



Genus Metacystis Cohn. Oblong; ciliation general, except poste- 

 rior end; ciliary circle around cytostome; usually one caudal cilium; 

 with a large posterior vesicle containing turbid fluid. 



M. truncata C. (Fig. 268, h). Elongate, not much difference in body 

 width at different levels; with about 12 furrow rings; body length up 

 to 30/i; salt water. 



Genus Vasicola Tatem {Pelamphora Lauterborn), Ovoid with 

 caudal cilia; lorica flask-shape, highly ringed; cytostome at anterior 

 end, its lip with 4 rows of long cilia; body surface with shorter cilia; 

 macronucleus round, central, with a micro nucleus; contractile vacu- 

 ole near macronucleus; fresh or salt water. 



V. ciliata T. (Pelamphora butschlii L.) (Fig. 268, c). Body about 

 100m long; sapropelic in fresh water. 



Genus Pelatractus Kahl. Somewhat similar to Vasicola; but with- 

 out lorica or caudal cilia; with a terminal vacuole; without lip of 

 Vasicola; sapropelic. 



P. (Vasicola) grandis (Penard) (Fig. 268, d). Free-swimming; 

 elongated fusiform; numerous contractile vacuoles on one side; body 

 125-220^1 long; sapropelic in fresh water. 



Family 3 Didiniidae Poche 



Genus Didinium Stein (Monodinium Fabre-Domergue). Barrel- 

 shaped; one to several girdles of cilia (pectinellae) ; expansible cyto- 

 stome at tip of cone-like elevation at anterior end, containing long 

 fibrils; macronucleus horseshoe-shaped; contractile vacuole pos- 

 terior; feeds on other ciliates; fresh or salt water. Several species. 



D. nasutum (Miiller) (Fig. 268, e-g). 80-200// long; endoplasm 

 highly granulated; with 2 girdles of pectinelles; feeds on Parame- 

 cium; fresh water. 



D. halbianii (Fabre-Domergue) (Fig. 268, h). 60-100^ long; a 

 single girdle of pectinelles near anterior end; fresh water. 



Genus Mesodinium Stein. Ovoid; an equatorial furrow marks 

 conical anterior and spherical posterior parts; in the furrow are in- 

 serted 2 (or 1) rings of strong cilia; one directed anteriorly and the 

 other posteriorly; with tentacle-like retractile processes around the 

 cytostome; fresh and salt water. 



